Honestly, I couldn't care less. As "fat" as he is, he's a player I wanted on my team. So whether he reaches his goal of losing the weight or not is of no real concern to me.
I can hope, so that we can see a potentially superior Sullinger, but his weight really holds little weight (pun intended) in my desire to keep him around.
We'll see how much his market price is after next season, that will be the determining factor regardless, and how we are setup when the time comes.
Of course, if an attractive trade comes along then so be it.
But I'm really not overly concerned by this. It will not make or break this team in any form.