when do you know it's time to leave your practice?

Have a solid job as an associate making between 285k-300k a year but it's a lot of work. A lot of work as in I see 15+ patients a day, work 6 days a week, and commute to multiple offices. I work in a very heavy peds mediacaid office and the money has been nice but I find anytime i try to cut back my days i'm met with a lot of push back. I was told by a more senior dentist once "if you're in a practice where you find that you're the life line of the practice that's when you should leave". How true does that statement resonate for any/many of you? I'm scared to leave a job where I make a very comfortable amount of money but I can't see myself doing this forever.