If Republicans in the House quickly line up behind McCarthy as a replacement for Boehner, it will show that they have learned nothing. It will show that they have mistakenly concluded that Boehner, personally, was just an unjust victim of Two Minutes’ Hate from the voters, because McCarthy is cut from exactly the same cloth. While he might not be as orange or cry as much, there is no chance that he would hold the line where Boehner has failed to do so.
One assumes that the coup that finally brought Boehner down would not have gone forward if McCarthy had not clearly signaled to Boehner in some way that it was coming, or that he did not have the rest of the leadership team behind him. And presumably McCarthy would not have given that signal if he didn’t believe that he had the votes to win a quick replacement election.
Probably, the way this is supposed to play out, at least from the standpoint of leadership, is that Boehner will, as his last act, fall on his sword to negotiate a clean funding bill that prevents a shutdown and provides for a debt limit increase. He will rely mainly on Democrat support. McCarthy will be allowed to pretend that he is opposed to this plan, while he counts the votes to make sure enough liberal/swing district Republicans are on board to make sure it passes. And then when this is all over, Boehner will be the appointed scapegoat and McCarthy will count on having a couple years of goodwill from the Republican voting public to try to get the caucus in order again.