They will recast him... just like Patrick Stewart was just in Dr. Strange 2 as Charles Xavier, but you know if/when they introduce MCU Prof X, it will be a different actor.
Same with Reed Richards, etc.
I mean we just had three different Peter Parker's in a Spiderman movie.
They are building too a multiversal war, so things will probably get pretty screwy before the crescendo.
I doubt Deadpool plays a large plot in the main storyline, but he can riff off of it to make the peices fit.