re: At some point self preservation is going to kick in for individual house Dems

This would be the logical scenario (and what I believe would happen if the parties were reversed):

The 30-something Reps who will be running in Trump districts should band together and tell Pelosi / AOC / radical wing to stick it. They will all vote "present" if she brings Impeachment motions to the floor. Even if they personally support Impeachment and think they could survive such a vote, they are standing in solidarity with their colleagues in brighter red districts.

This could happen behind closed doors obviously - but if the 30-something all stand together (even though probably 20 of them would vote to impeach) none of them can be treated too harshly by the radical wing of the party.