I think the only way he doesn’t run again is if he dies in office. I think he’s miserable with the job, he hates being president, but his ego won’t let him quit.
To address your individual points:
There are two ways this may occur. Indictment or impeachment. As you say, any attempted indictment will almost certainly have to go to the Supreme Court. Roberts is the only conservative justice who I think might allow the indictment to proceed, and who knows how he’ll vote.
Impeachment is a non-starter. The Republicans will never do it.
Prosecutors may very well target Trump’s family if they have committed crimes. I don’t see what that has to do with getting him not to run for reelection. Prosecutors are not likely to drop the charges against his family just because he chooses not to run.
Maybe you mean Trump will plead guilty in exchange for having charges against his family dropped. Prosecutors would agree to that, and it would likely result in Trump not running. But I don’t see that as likely to happen. I don’t think Trump is likely to put even his family ahead of himself.
This is the least likely of all. Trump still has a 90% approval rating within the Republican base. The RNC and congressional Republicans are not going to turn on him so long as his numbers are that high, because the voters will turn on them. They’ll start to get primaried.
But suppose that the party does turn on him. Given the size of his ego, I think he’d still run anyway, out of spite.