I think Scioscia, Gardenhire and Leyland should come back next season, if they want to. Valentine and Ozzie Guillen should be able to return to their respective teams, if they wish. Replacing Terry Collins in New York will do nothing if the front office has no plans to improve next season. All that being said, I would not be shocked if Valentine, Guillen or even Collins was replaced after this season. (Though I would not agree with the decision to move any one of the three.)
I think it was fair that Brad Mills finally got to leave the Astros. It was almost unfair what was done to his team from the time he took over. As the Cleveland Indians continue to give up on this season, it should spell the end to Manny Acta's tenure. They currently sit at 63-90, in last place in the AL Central. This was a team expected to be in the postseason discussion, especially with the second wild card in effect. This is a situation where the manager has to take the hit. This team had expectations after a good season managed by Acta in 2011. A change in leadership would be a good sell to the Indians and their fans. Acta will get another job as manager.
The Colorado Rockies have been hit with an unfair amount of injuries this season. But the fact that they currently sit 36 games under .500 is unacceptable. Jim Tracy has to go after this season; there is too much talent on this team to be among the worst in the game in 2012. I think this is a team that needs a new leader (and to go back to the old pitching philosophy). Hopefully the Rockies don't choose to keep Tracy around as long as they kelt Clint Hurdle. Somebody has to be held accountable for this failure. The Rockies were a legitimate wild card contender coming into this season.
Finally, I think the plug should be pulled on Ned Yost in Kansas City. Perhaps he gets to start the 2013 season at the helm, but there is too much talent in that organization for the results to not be better. 70-82 is not that bad, as Valentine, Gardenhire and Collins can tell you, but the Royals may look in places like Baltimore and Oakland where teams with less blessed farm systems have put it together.
One thing Acta, Tracy and Yost have in common is that they have all beenin their current positions for a little while now. None have established themselves as good managers. None could have the story told they did more with less. Perhaps others will lose their jobs after this season, but to me it starts with Acta, Tracy and Yost. Acta and Tracy definitely, Yost most likely. And Valentine and Guillen, only if they want out.