I think FTP kind of plateaus, but you can work on it a bit. It seems that the rider gets better at the test, not necessarily stronger, at least that's my experience. I pace better, minimize my 12 minute mark "slow down", and aggressively use up anything I have in the last couple minutes. That is when I actually finish the test. Usually I stop after a few minutes.

After about 3 months off the bike (Aug - Nov), I was really weak, like 100w vs 200w. I was also dieting aggressively. By late Feb I was back to July levels. That level doesn't seem to change much no matter what I do (hello, genetics!). So it took me 2.5 weeks of lots of steady riding ("training camps") and a bunch of trainer rides in the basement to get back to where I was in the previous July.

I dunno what that means but that was my experience. 3 months of JRA, with maybe 10 long rides (3-6+ hours) and I was back to normal. I didn't work on sprints per se but my sprint was 90% of what it's been by first week of March. I think sprinting is genetic too.

I'm already thinking of next year too. I may not be able to race as much, but talking with the wife she supports me racing as much as possible. I've been putting off buying my back up frame because of my doubts for next year. I was also putting off requesting an upgrade. But I may/probably-will do both in the next month or three. I want to do another few months of strict dieting too, goal being sub 145 lbs (10-15 lbs loss). I figure my strength won't deteriorate much once I've lost the weight, but the hard part is losing it. I'd be about 40-60 lbs lighter than 2 years ago (!! - used to be 180 min 210+ max). Should help if I end up upgrading.