With all the R senators backing him in the "election fraud" fight, is there a chance he won't actually leave in January? That he could manage to invalidate the results somehow and/or throw us into leadership limbo for years with a prolonged court battle? It's such a scary thought!

I don't think so. Several GOP senators have either already congratulated him or affirmed that he won. James Lankford (Oklahoma) just said today that if Biden doesn't start receiving Nat'l Sec. briefings by Friday, he will step in and make sure he gets them.
Over my dead body.. and I think millions feel the same way. We would storm the WH. I'm hoping he pushes it too far and gets charged with treason for attempting a coup.
Emily Murphy, administrator of General Services Administration, still refuses to affirm that Biden won the election.
https://www.nytimes.com/2020/11/09/us/politics/emily-murphy-trump-biden.html
I posted before that I was scared about his supporters rising up
No. He is going to capitalize on this to raise as much money as he can, and then slink off to Mar-a-Lago and play golf (until the Manhattan DA places him in handcuffs).
This is meant as a lame joke - ”all the wrong people are already armed for the civil war”.
He could very well incite a civil war. Nothing is absolute, not even the constitution or our democracy. It's only as good as our implicit agreement that it is.
All the smart people say not to worry, but we're still in the Trump Era. Anything is possible.
No, there is no chance of that happening. He can litigate all he wants, but if there is uncertainty as of January 21, then Nancy Pelosi as speaker will become president :)
I'm not an attorney, but my understanding is that they would need to present evidence of voter fraud. I don't think they have any.