There isn't a cat-in-Hell's chance he'll accept an actual defeat. [/quote]
He might not accept a defeat, but if he is then there is eff-all he can do about it. He can try and delay it or, if that fails, lock himself in the Oval Office, but under the 20th Amendment, his term of office ends on January 20th, election or no election. Protection will be stepped down (other than that which is granted to ex-Presidents), nuclear codes are changed, the guy with "the briefcase" leaves his side... And as was made clear a few weeks ago, the armed services serve the Constitution, not the President, and they will remove him by force if needs be.
He'll go. He won't go quietly, but he'll go (assuming he doesn't manage to rig the election first to stay in office another term).