Can I retain the majority of my current running fitness with less MPW and what would that look like?

Hello. I’m thinking about reassessing my running program. A quick background on me. Im about 185 lbs, 36 years old, and I’ve been running around 8 years. I’m physically in fine health, but I’m wondering if my volume of running is still appropriate for my goals. My planned goal is to scale down my miles volume to the minimum needed to maintain the fitness I’ve already built. It’s nothing special: avg pace around 8-8:30 minutes per mile, around 19 minute 5k or so. I currently do around 40 miles per week with a 12 mile long run on Sundays. I know the answers will be there are a ton of various factors due to individual differences from runner to runner, but in general, what sort of MPW do you think I would need realistically to maintain what I have? I’m not racing or anything anymore; I just don’t want to lose the high metabolism and health benefits I’ve gained from 8 years of hard work.

TL:DR “Can I still get the majority of my current running fitness with less MPW and what would that look like?”