"not beyond the realms of possibility" is, sadly, so vague as to be meaningless. A better question to ask is why the Democrats who are supposed to have rigged this election forgot to do the same in the Congressional ballots, which have gone pretty badly for them (losing seats in the House when they were expected to gain, and failing to capture the senate).
A slightly more plausible explanation for what we've seen is that enough people dislike Trump that they'll vote him out personally, even if they still consider themselves Republicans (or, at least, not Democrats).
As to your second paragraph, I'm not sure either explanation is right. The second feels particularly strange: the logic of saying as little as possible during an investigation, refusing to concede, etc, I can certainly accept, but "saying as little as possible" is clearly undermined with his own constant tweeting, not to mention various officials spreading the word on his behalf (McEnany etc). Or that "press conference" from the White House a week or so back, where he took no questions whilst alleging major fraud. What I mean is that if this is his strategy then he's doing it badly, and should say nothing at all, even on twitter.
The first -- well, maybe, but I'd offer an alternative explanation, which is that Trump, a man who's built his career and persona around "winning", can never accept that he has lost, and is looking for anything possible to destroy the legitimacy of that defeat, at least in the eyes of his supporters. It would be enough to kick up a fuss and then go, when he must, grudgingly, in order to be able to sell the idea that the system was rigged against him so he didn't really lose, etc etc. Either that sets the platform for a 2024 campaign, or for a future pitch along the lines of "Your REAL President Speaks TV".