Well, this would be amazing for Buffalo. As much as I like the prospect of Drew continuing to play with Ennis, Krejci is a legitimate all-around center and we're a team that is going to be depending almost entirely on young centers over the next few years (current players + guys like Grig/Zemgus/Cat/Sundher coming up) barring any additions. Brennan is basically a throw-in from our perspective as he likely has no role on the team going forward, though he has value for other teams as he probably will be a solid NHLer.
Can't see this happening at all, unfortunately, but it was fun to imagine.