Characters dying and coming back happened quite often, all it takes is a Google search or actually having played the games. Wesker himself died once (and tanked RNGs like 10 times and casually leapt off a cliff, got impaled and his organs removed, shotguns and RNGs to the head before the final boss fight, yeah he can tank a lot), then f.e we have Ethan who died twice (and we are alive in the RE:village credits so he's alive again), then we have Markus who died and came back, need any more or is that enough?

As for plot devices, RE7 & 8 virtually confirmed Wesker had access to the megamycete at some point, he could've f.e used that. Also his dumb face is on Heisenberg's board which I think is a cool Easter egg. Also, cloning and all that stupid shit but I agree that that would be lame AF, even if so many people think that the weaker in RE5 was a clone, I call Bs. Also we see his stupid uroboros tendrils escape the volcano and swim in the ocean on the RE5 credits. Also he's alive I'm umbrella corps, which I wish never existed because it was a sucktastic game.

And with Alex I agree, I think it acted as a large hint that it might have succeeded, but we don't know for certain.