Buffalo is one of the few teams that really doesn't need Marner. Savoie is basically another Marner (if he reaches his ceiling), or more realistically, a Marner-lite. Buffalo's biggest need that they don't have a prospect coming for is a top pairing or at least top 4 right hand D to play with Power that can provide good defensive play. They also need a goalie good enough to win them a cup, but between Luukkonen and Levi, they might already have that. Time will tell.
The only other team need I can really think of would be a high end power forward type winger. They have Tuch already, but in an ideal and perfect world, they'd have a young prospect coming along to replace him in a few years. Buffalo has most of their ducks in order, as compared to the rest of the league. They really just need the RHD to play with Power, and to translate their talent into winning games.