Not decay as they would be frozen, obviously.

Sublimation. As long as it gets energy from radiation some atoms or molecules would randomy get enough to f off into space. In my theory, at least. And bones would stay last as they are the hardest.

Sublimation happens all the time. I got that from AlphaPhoenix on youtube https://www.youtube.com/watch?v=bnqQyeqGIBE Really cool science channel