He'll never go away. I predict that, no matter how or when his presidency ends, he will ignore the near-unbroken tradition of former presidents staying quietly in the background. He'll conduct a shadow government where he'll tweet and send out spokespeople constantly to say what he would have done differently, how the person in office is only there due to lies and media bias against him (even if he serves two full terms), and braying about his latest pet conspiracy theory. Imagine it's 2030 and Trump is still watching far-right "news" and claiming there are servers the FOX had shipped to China full of detailed plans to undermine him.
I almost pity Mike Pence. If he inherits the office, he'll want to bring some sort of order and structure back to the federal agencies. Yet Trump will be calling in to some tv or radio show bemoaning the fact the Pence is betraying him.*
*I don't actually pity Mike Pence. He tied his wagon to this particular star and it would only be the tentative beginnings of justice for former president Trump to turn on him.