I had mine since dec 2001, he died last week. I still don't know what cause him to deterate in the first place, I messed with the sg, it was way too low and he never recovered...
However, stars can regrow. Mine did the first time. We moved, the water spiked, he's legs shrunk, he stayed in the lr, didn't get when I'd try to feed it. I kept the lights off on his side of the tank and left him alone, a few months later he legs went from 3 inches to 6 inches, and he was bigger than before.
What are your water parimeters?
Check you water, am, nitrites, nitrates, ph, alk, sg, temp, ect. When was your last water change? Any change in the water lately? A sudden change can cause stress, which you may not see till a little while later.
Has they been any change in your tank? Anything to stress him out? Is he eatting? When was the last time you fed him? Have you tried feeding him lately? is someone bothering him? is he acting different? Is he losing legs, dropping the actual leg, or just getting smaller?