Regarding the pertinent issue of Trump (should he lose) refusing to concede, three points:
1. Remember that it is not necessary, legally or politically, for the losing candidate in any American election to concede. Cleveland didn't need to concede the World Series to make the Cubs the winners.
2. In the event that the outcome is not especially close, any attempt he makes to contest the results will have little effect. The Gore-Bush thing got drawn out to the wire because there was a single state at issue with a margin so thin that the odds of such a finish recurring are almost vanishingly small. Contesting the results in like fifteen states at once, especially if the popular vote is not particularly close in most or any of them, amounts to nuisance litigation and one last pathetic publicity stunt. That strategy has zero chance of succeeding.
3. In the event that the election is not a blowout but the difference is anything greater than "Florida 2000" close, I'd bet that the Republican National Committee (possibly relying on Pence, who is effectively estranged from Trump for weeks at this point) will concede the election and wash their hands of anything Trump does moving forward. One assumes they are in full damage mitigation mode right now and, at the very least, committed to ensuring that he does not tarnish the brand any more than he already has.