I think elements of Trump's politics will have staying power even if he loses the election, but it's premature to say exactly which ones. The safest assumption to make is that if we are really heading for a realignment, then things are going to be complicated for a while. At the time of the southern realignment, there were still socially conservative southern democrats running alongside liberal north-easterners.

Similarly, I think in the immediate future, there will be a "Trump Coalition" in the Republican party, united most strongly by a hard-line stance on immigration. That said, there hasn't been a mass exodus of establishment Republicans from the party, let alone to the democrats. These traditional Republicans will battle for preeminence with Trumpers and I'd hesitate to declare a long term winner until one or the other leaves in large numbers.

One thing to keep in mind is just how spineless and unprincipled most of our elected officials are. They read polls like religion, and jump on any prevailing trend, desperately clinging to relevance or their office - witness the easy acquiescence of the NeverTrump movement, or people like Christie and Gingrich abandoning their closely-held positions in order to jump on the flavor of the day. The vast majority of those in office or seeking it will keep their head down, focus on opposing the other side and then adopt whatever ideology emerges victorious. I actually don't think the parties of 2020 will be very different politically from 2016, regardless of who wins this year.