We have NO small forward to backup Pierce if Green goes. We need him, and we really need a 'jack of all trades' player off the bench who can do a little bit of everything - score, grab some boards, play some defense, run the break.
Terry is going to be our primary scorer off the bench, but while he will get the occasional assist, scoring is really gong to be the main commodity he provides.
Lee is mostly a spot up shooter and doesn't really do a lot else aside from some maybe play solid defense (I've heard mixed reports on that).
Sullinger has talent but is unproven, Wilcox can be very solid but isn't dominant, Darko and Collins are...well they are Darko and Collins.
Without Green we have a solid bench, with Green we have an exceptional bench. People may say he's not that great, but even worst case scenario (at the worst we've him) he is elite by bench player standards...and we need that. Best case scenario a fire lights under his but and he brings out some of the potential Doc and Danny have always seen in him, and then he earns every cent.
He and Terry are the last guys I want to trade outside of Pierce, KG and Rondo because they are the guys who are going to be the leaders of our second unit. If those two guys can be elite bench players it takes pressure off Lee, Sullinger, Wilcox, Collins and Milicic to be able to just play their game rather than trying to do more than they are comfortable with.