He should be fired but not because of the Hall trade. He actually got an important player back for Hall, it's the moves like the Reinhart trade, Eberle trade, Lucic and Russell contracts (the ridiculous NMC for Russell) that hurt the team more.
I'm happy for Hall but he wouldn't have been Hart level Hall in Edmonton. Sometimes players need a change of scenery to get the most out of their abilities and this is one of those instances.
Hall may not have been Hart level if he stayed in Edmonton, but I still think he would've upped his game on a Oilers team competing for the playoffs. You can see how badly Hall wants to finally get into the playoffs and that's been a huge motivation for his high level of play.