Unfortunately, he's exacerbating the problem.
We have a problem with Trump and his followers having too much sway in the party, so we leave and give them a bigger slice of the pie?
A lot of Trump supporters weren't even Republicans until relatively recently (think Santender), and I'll be damned if I just fork over a party I was in first.
You hit the nail on the head here. One can do more fixing the GOP from the inside than there is by ditching the party and essentially allowing Trumpists to take it over.