The image of Trump refusing to vacate after losing the election may be farfetched and unprecedented, but those two adjectives describe the entire Trump Era.
A few observations, in no special order:
1- SCOTUS, in Bush v. Gore, voted 5-4 to halt the Florida recount and install Bush as President, with all 5 Republican appointees joining in the decision and the 4 Democrat appointees dissenting. The court today is more conservative.
2 - Trump said at the final debate in 2016 that he would not necessarily accept the reported results of the election. He stated at his first Presidential press conference that he had indeed won the popular vote over Hillary, but that fraudulent votes had given her a majority. Since he is already making noise about fraud with mailed-in votes, he will naturally complain if he loses that the increase in mail-ins demands an investigation. He has an AG who backs him with extreme partisanship. So, is it simply a fantasy that Barr would compile a case for the Supreme Court that demanded that the election results be set aside so that a new process could be put in place to certify the election results in the various states? Is it unthinkable that the present court would consider the case and rule for Trump?
3 - The man himself would have no problem whatever throwing the country into disarray. There is no precedent for Trump in our history. Please tell me what would restrain a man who has already done away with norms of Presidential behavior ('shit', 'son of a bitch', goddamn' are now terms of Presidential public discourse; he relishes speaking ill of the dead, implying that Rep. Dingell is in hell, that Lori Klausutis was murdered, and that John McCain doesn't deserve his respect, caring nothing when their families ask him to stop; eighteen thousand documented lies and counting, including six full years of Birther lies) and more to the point, norms of legal and ethical governance (writing a $130,000 hush money check, paying a $2 million fine for running a fraudulent foundation, paying a $25 million settlement to make his diploma mill scandal go away, requesting political intel from foreign governments, defying Congressional oversight, calling for war crimes, pardoning convicted war criminals...) I know I'm leaving a lot out, but these come to mind straight away. The man is a cheerful degenerate.
To contest the election (if nothing else, for his own ego), he would need Barr on his side, and that's a given. He would then need to have a case submitted to the Supreme Court. That's a gamble Trump might take. Helpful quote: "Then I have Article 2, where I have the right to do whatever I want as President."
No, this is not a normal scenario, but Trump's presidency is completely abnormal. The institutions that should block the actions of an out-of-control executive haven't been all that vigorous so far.