But it would require an historic loss in November, losing maybe 60 seats in the House and 3 or 4 in the Senate, so that they are scared to death for 2020.

Of course, there is no guarantee that Trump wouldn't go down swinging or threaten to take them down with him (depending on how much the other Republicans knew).

Plus, a pardon is still going to be pretty unpopular, and I doubt the Dems are going to drop the investigation if they take the House in November.

That way, Pence can serve for almost 10 years, instead of a little more than 6.

edit to add:

... the horror ... the horror

See Gerald Ford. It wasn't just that he pardoned Nixon, he also wasn't a very good President, his primary qualification being that seemed like a decent fellow and not a crook. Pence might not even have those two things going for him.

Pence is likely dirty. With democrats controlling the House, both him and Trump will get the investigative treatment they deserve from Congress, and Hillary or Nancy can step in as national reconciliation leader of the country.