…At least his legs are okay?
It’s popular opinion that Wesker was completely compatible with Uroboros, and therefore would have been able to return to normal had he not perished via lava/rockets. Suck it all back in, if you will. Akin to Alexia, he had some control over what form the black wigglies took and I think it was only his weakened state that had him a little unstable. It wasn’t a point of no return thing, like Birkin.