A lot of the fire breathers and ideological bomb throwers that jumped on the Trump bandwagon in order to burn down DC would not find Pence as attractive. No doubt Pence would shore up the conservative Christian vote which is beginning to crack as the moral dissonance has become too much for some. But the populists don’t find Pence as energizing. As a consequence many Republicans who feel that they are hostage to Trump and his horde would not be as inclined to follow Pence as blindly.
But that said, if the Dems can get one chamber of Congress, keeping Trump in office and spending the next two years after the mid-terms dragging him through hearings and finally impeaching him midway through his fourth year would be the perfect outcome. This would deprive Pence of any political oxygen. Totally tarnish the Republican brand. And leave Pence and the Republicans very little time to recover before the next presidential election is upon them.
For those reasons I have a long shot bet that if the Dems take both houses the Republicans who lost their seats may make a move to impeach just to avoid a protracted round of hearings and get their guy Pence in place with plenty of time to do damage control before the next election. The Dems would feel pressure to deliver on impeachment. The Repubs would want it over quickly and hope to defuse the energy of the Dems so they can build their case before the next cycle.