Well you can infer many reasons for Tom being out. I think that Mike did want a legitimate front for the things that he was doing in Vegas. I do not think that he ever blamed Tom for Sonny's death, I think that he (Tom)did enough of that himself. If you remember that Don Vito tells him that he never thought that Tom was a bad consigliere but that Sonny was a bad Don. I think that Tom was a wartime consigliere but that he was not prepared that Sonny would go all out like that because after all Tom did tell Sonny that shooting the old man was not personal it was business in GFI. I thinkt that Mike wanted to keep someone on the outside that he could trust with what he loved the most and that was his family if you recall the conversation that they had in Nevada after the assassination attempt. After that when Michael left to go to Florida and Cuba he left Tom in charge. So in all reality Tom is never really "out". I think that was just something to see how loyal Tom really was.

Corleone256