Semper's Stupendous to Infinity and Beyond Everything Marvel Movie/TV Thread
If they have to recast, I *think* the only thing in the can or even in production with him still as Kang is Loki season 2. They could conceivably find a way to replace him going forward, especially since their film slate is allegedly getting massively reshuffled in the wake of Iger returning and Quantamania sheetting the bed.
The immediate stuff coming out (The Marvels and GOTG Vol. 3) doesn't have him in it. So they do have time. They could even conceivably do some reshoots on Loki to explain the change, although who knows if they get money for that. Disney is in hardcore cost cutting mode.