That's definitely a young person's undertaking. I can see this as being possible. With filter cleanings/changes and oil changes as required, the motor should still have service life remaining, at the end. The biggest hurdles will be international border crossings and sourcing parts quickly, should something unanticipated break along the way. That's a lot of miles for any bike.
Still, there were two riders who successfully completed a ~19,000 mile ride along the west coasts of North & South America, circa 2002...on Cub 50s.