Meh. Keep 'em. The Bruins have Fabian Lysell who was drafted at the same time as Rosen and is putting up a better year in the AHL and I'd say he's developing about where he should be for a mid-20s first rounder. A guy picked 14th should be looking better, not worse than him.
As for Middlestadt, he has well-documented issues with his work ethic. He's on pace for 49-points this year and currently playing on 3rd line so "will score 50+ this year" is overstating things. He also ranks at the bottom of the league defensively and racks up points on the PP. So he's not a 3rd line center and he's not a top-6 center. Exactly why do I want him at all? I'd rather sign a guy like Erik Haula for $2.5m in the offseason.
Admittedly, goalie values are tough to pin down but I don't see why the Bruins have to do anything. The absolute most that Swayman will make is $4m x 3 like Oettinger. I'd rather have two great goalies.