Personally wouldn't trade him for anything short of a top 10 pick yet, but if they ended up going that route it would depend on who they take.
I haven't been following these draft prospects as closely as I have in past years, but I've tried to read a little bit more lately and I keep coming away less and less impressed by the centers available, and trading Rossi+ to move up in general. Lots of guys who are either too slight to be a good bet to even end up as a center in the NHL, or guys who just don't seem to have the offensive upside to be a top six center. Just trying to piece together our realistic pool of options if we trade up to the 10-15 range... Moore, Dvorsky, maybe?... Yager, Danielson, Ritchie, Heidt, Brindley, Stenberg, Stramel... It's not that any of these guys aren't good or couldn't be a top six center, but how many of them are more certain bets to be top six centers than Rossi to the point where you trade Rossi+ for them? And how many of them could we still get at 21 or later?
I'm shifting more towards keeping Rossi and using the 21 (although I'd love to somehow keep this and add another first on top of it, but we're running out of ways to do that), Addison, the 2nds to try to move up and get another one of these guys who are usually ranked anywhere between mid first and early second round. I feel like if the quality of player we're going to get at 12 or 14 or 21 or 25 is fairly equivalent, maybe we're better off keeping more of the darts, including Rossi.