I think its very possible for players to come back and achieve the same success, if not more than before they retired.
It is, however, unlikely that said player will ever find the drive/commitment again.
Of course, whenever players take a break for say, 3 or 4 years, they are coming back to a very different game. Metagame changes, old strategies no longer work, and returning players need to play "catch up" to get back to the top, so yes, its very difficult, but its not impossible.
I think that if Chu had kept working at it, he could climb his way back up there.
And he was successful... he got 3rd at a regional, had a very close set with M2K, etc...
he proved that people can come back and be successful, he just didn't follow through with it.