There's a big difference with this situation. Farage formed his party over a single issue, thereby forcing the Tories to back Brexit (it was the Conservative party that just about collapsed, not Labour). As long as Farage got Brexit he was happy, and UKIP had served its purpose. With the Republicans there is not one single issue.
There is a general philosophical divide between the wings of the GOP. Arguably it goes beyond philosophy to differing perceptions of reality and personality types. I believe that the typical establishment Republican reads the NY Times, and mostly believes what they're reading, while rarely looking at conservative sources. This is why they don't think the election was stolen.
“Farage formed his party over a single issue,”
Not entirely true. The UKIP was/is in large a party that brought issues that favored the UK. Brexit being the main issue being that most everything was tied to the Euro cabal.