Here's my take on the firing:
Guerin is telling the players that it's up to them and he wants to see exactly what players he has going into the future. The experience/structure/protection of an experienced coach are gone. Firing Bruce now guarantees Guerin will learn something about this team in the final months, whether good or bad. There's only so much a coach can do, at some point the players need to motivate themselves. That's what Guerin is trying to figure out. If he had no intention of extending Bruce, makes sense to let him go now.
Evason is simply the guy who gets the title of "interim". IMO, Evason was told the same thing: its up to the players now (explanation for deferring to players late in Saturday's game). I bet Evason will take a hands-off approach all year (because that's what he was told to do). Win or lose, Guerin wants the rest of the season to be a productive building block for the future. Win some games, great. Build some "hope" for the future with the guys who are catalysts going forward and fill some gaps around them. Lose every game the rest of the season, great. Pick up a couple assets in the draft and do what you can to rebuild the roster.