If they're really going to bring in quality hitting instruction, actually give these guys an offseason plan, and make sure they stick to it, then I'm fine keeping Vaughn for one more year. He was a consensus top 5 draft pick that year I believe, so it's worth giving him a real shot with proper help after they epically bungled his growth plan.
If they're not going to do these things, and just count on him fixing himself, they might as well let him go. Also if they determine he's just ruined or a bust, then they might as well let him go.
Either way, what a disappointment he's been and I don't particularly care if he stays.