Couldn't he literally order Air Force One to fly him to Russia on Jan 5, 2021 (or pick whatever date before new term starts) and leave w/o him? Among other less outlandish "brazenly waltz right out of U.S. custody before losing power" schemes?
Maybe. He has property/money all over the world to go after. Cut off his bank accounts. Most countries would also be willing to arrest him and send him back.
He also has till January 2021.
If things look like they're going to the crapper early enough, he'd have plenty of time to wind down and liquidate his assets. I'm sure he'd still lose a lot of money, but I doubt he'd be anywhere close to penniless.
It would be impossible to do that without being noticed.
would he care if it's noticed?
At that point, he's clearly broken the law and going to jail and the only thing preventing that is him being president.
He really has nothing to lose at that point just blatantly doing illegal financial shit while he still can, to salvage as much of his wealth as possible.