I think they'll do something similar to what Arrowverse did with their Crisis on Infinite Earths. Some earths (for example MCU and Fox, F4, and some more) will combine with each other which will result in a new earth with rewritten history in which all those people who were transported always lived there. It will also result in new heroes and villains. That's just my idea of what they might do, which sounds more likeable than rebooting the whole thing and making 19 years of movies and shows pointless. If they sticked with Kangs instead of replacing them with Doom, it would've been a good way to introduce him in the MCU.