The DEMs aren’t losing the House in 2020. I would be more concerned about the GOP losing the Senate in 2020.
I don't see a scenario where Trump wins in 2020 and we don't win the House.
In 2016, with Trump on the ballot, we won the House 241-194, with the total popular vote being 63,173,815(R) 61,776,554(D)
We lost the House in 2018 because Democrats had better turnout 60,572,245(D) to 50,861,970(R). Notice, a LOT fewer Republicans showed up than in 2016.
In 2020, turnout will determine who gets all the marbles, as in 2016. Turnout will determine everything.
I don’t see how the political climate could be that Trump wins and the Dems win the House at the same time. So you are writing off everything?