Which Big 4 members are likely to stay involved in the tour as coaches or commentators?

I can see a really old Federer taking over Rod Lavers role, handing out salms etc.

Nadal becomes a supercoach at his academy and brings out lots of fine tuned talent.

Murray coaches Stefan Djokovic and one of Federer's daughters, who are married and dominate the mixed doubles.

Djokovic becomes 15. Dalai Lama

I don't think any of them will be coaches. The only reason they would do it is if they get bored. Roger has a huge foundation so he will definitely focus on his philanthropic work. Rafa has a tennis academy that he will be very invested in. Djokovic I'm guessing will do some humanitarian work for Serbia. Murray will do whatever it is that British Wimbledon champions and gold medalists do.

I think that Murray would make the best commentator, and Djokovic would make the best coach.

Federer:

Coach: I think Federer would be a great addition to a team from both a tactical standpoint and a mental standpoint. He has an all-around game and his playing style has evolved and shifted over time. I think he’d advocate for a more aggressive style of tennis with more coming to the net. He’s someone that has been to the top, had some stumbles, and rose back up again while staying passionate about the sport. I think he would fit more of the temporary partnership style of mentoring rather than long term coach to get promising players over the hump. He could coach players with a variety of styles, but I think he’d be best as an addition to a player looking for advice on how to get more aggressive. He’s had multiple people on his coaching team include former Sampras Coach Annacone, Stefan Edberg, and current coaches Luthi and Ljubicic. Given his long career and multiple kids, I don’t expect to see him coaching right away or traveling on tour for long periods of time. Maybe after a decade or two once the kids are gone.

Commentator: Again, Federer would be a great commentator and tennis personality. He’s fluent in multiple languages, has been poised and talkative in interviews, and clearly still has love for the game even after a long career. I could see him doing spots as a guest commentator during some GS tournaments or at Basel.

Other Roles? Federer has always been a presence at his home country’s largest tournament, the Swiss Indoors in Basel where he was a former ballboy and won 7x. We could see him taking a larger role in organization and promotion, or with the Swiss Davis Cup team. His representation of his country at Davis cup games has been inconsistent given their lack of supplementary talent for much of his career, but he did commit to partnering with late bloomer fellow countryman Wawrinka to win the country’s only Davis Cup title in 2014.

Nadal:

Coach: I think Nadal’s interest in coaching might be less clear. I’ve always thought that Nadal is more of a private individual. For most of his life his coaching team has been centered around his family, specifically his uncle former professional player Toni Nadal who started coaching/training him at the tender age of 3. Only this season has he added Carlos Moya to the team with Uncle Toni transitioning out of following him on tour. Nadal is certainly a legendary player and the best clay court player and in the argument for GOAT. He has a very physical heavy topspin style and dogged court coverage with aggressive shotmaking from the baseline. If he coaches, I’d see him looking more to nurture a young talent long term than do temporary partnerships to hone an individual.

Commentator: Nadal has made leaps in his public speaking abilities since coming into the spotlight as a teenager, but I don’t know if he’d be a great fit for commentating. To be fair, I have not watched many interviews of him in his natural language.

Other Roles? Spain has a couple high profile tennis tournaments, Masters 1000 Madrid Open and 500 series Barcelona Open. I’m not sure which one the Mallorcan has more ties with. Mallorca is geographically closer to Barcelona, but Nadal supports RC Madrid for football. The Barcelona Open has named their center court after him and he’s always participated in that event, winning it 10 times. He’s also been a frequent representative in a multitude of talented Spanish Davis Cup teams, winning the title 4x over his career.

Murray:

Coach: I don’t know too much about Murray’s interest or fit in this situation. He’s been heralded as the next British hope for so damn long and finally got the monkey off his back with his win(s) at Wimbledon. There’s also that Scottish/British identity he has to juggle with the media. British if he wins, Scottish if he loses as the joke goes. He’s more of a passive and defensive player, but one of the best counterpunchers on tour. He’s had a multitude of coaches, the most famous of which is Lendl who has been credited with helping him sharpen up his mental game and rise to win slams. His mental game has been a question mark during large portions of his career, and on court he gets down on himself pretty often. He could be an addition to a team for specific players with similar playing style or to provide advice for help dealing with expectations and pressure.

Commentator: British media is certainly big in tennis and they have some top tier tournaments, notably Wimbledon. As the only living British man to win any Grand Slam, let alone Wimbledon, I imagine there will be offers out there if he wants it. However, I think with the level of criticism he’s had from British media at times throughout his career he might pass on being more than an occasional guest commentator for fear of scrutiny. Other Roles? Britain hosts 3 large tennis tournaments: Queen’s Club, the ATP Finals, and of course Wimbledon. Wimbledon is high profile to begin with, but we could see him promote Queen’s Club, the event he’s won 5x. His relationship with Britain’s floundering Davis Cup team has been tenuous at times. He’s skipped events multiple times and has received criticism from team captain at times for doing so.

Djokovic:

Coach: Djokovic has had an interesting history with his coaching team. He’s had a long list of tennis coaches, the most celebrated of which is a 3 year partnership with Boris Becker. He’s also had a dietician who diagnosed him as gluten intolerant, and he has credited a lot of his success to maintaining a vegan diet. Former player Pepe Imaz (who promotes the power of meditation and lengthy hugs) has also been a part of his team after curing Djokovic’s father of depression. As a player, he’s an all-around player that wears you down in baseline rallies. He’s had a stretch of all-time great tennis for the past half decade before sputtering out last year after finally completing a career Slam at the FO. Since then, he’s admitted to having lost his drive for tennis for a period, but hopefully he bounces back. I think his coaching style would be influenced by the conditioning work and meditation he’s been exposed to. He’s definitely had a top tier mental game during his peak, and hopefully after his recent funk resides he’ll be able to provide some insight into avoiding that as well.

Commentator: He’s always come off as a very open and extroverted person. He was booed at some tournaments for behavior on the court earlier in his career (including US if I remember right) and liked to try to please the crowd as a (D)joker, but he’s become more mature and more poised as he became a top player. I don’t know much about Serbian media, but I think he’d be more interested in developing Serbian tennis coverage than at a US or UK broadcasting station. Personality wise I think the mix of serious and joking nature would be a great fit.

Other Roles? His family already owns the Serbian Open, an ATP 250 event where he has won a couple times. He’s been a big figure in Serbia’s Davis cup team and was a key part of their 2010 title win. I imagine he will continue advancing Serbian tennis through a combination of both events.

All of these guys have been great ambassadors of the sport, and I hope that they will continue to have a role in the sport, large or small, after retirement.

I see Rafa being more involved in football and golf than tennis and I imagine the extent of his involvement in tennis will be limited to his academy.

Federer I can't see coaching or commentating (except for the odd guest appearance). He strikes me as more of an ambassadorial character for the global game as too many tennis organisations/broadcasters will want a piece of Fed once he retires and as such I imagine he'll end up just forging his own path.

Novak... goodness knows whilst his association with Pepe continues.

Murray, I don't think will coach any pros, but I do think he'll end up quite involved in trying to improve facilities and childhood engagement with tennis in the UK. I can also see him getting involved in trying to reform the LTA. I do think Murray could make a great (co-)commentator if he can get over his reticence about his voice and warm to the task. He can be a very engaging person away from the court and could deliver some great insights.

I wouldn't be surprised to see Andy coach a woman one day.

I could at most see Fed being involved through the Basel tournament in some way… maybe Murray as a commentator a little later

I often think about how, someday I'll be watching a tournament and a grey and wrinkled Nadal or Federer will be sitting in the crowd and I'll bore my son or daughter with stories of how great they were way back when.

I'm pretty sure all four will appear on BBC's Wimbledon coverage at different points after their retirements.