Even though the events of Resident Evil 5 make this obvious, Wesker has proven himself to have superhuman capabilities, and Umbrella’s other projects Tyrant T-103 (Resident Evil 2) and Nemesis have proven themselves capable of surviving immersion in molten metal, and in Nemesis’ case, being dumped into highly-concentrated acid and still hang onto life after a direct hit with a massive railcannon. However, he wont be in Resident Evil 6.
Wesker’s voice actor D.C. Douglas tweeted that he did not work on Resident Evil 6. He also confirmed this on his Facebook, stating once again that he did not do any voiceovers for the game. He has said that it looks awesome, and that he has other things coming, possibly as a voice actor.
There are theories that even though Albert Wesker wont be appearing following being sent straight into lava during the events of Resident Evil 5, the twelfth of the thirteen Project W candidates, Alex Wesker, may be in the game.
If you skipped out on Resident Evil 5 due to it getting rather lackluster reception, I recommend reading these wikia articles so you can brush up on the lore and canon that you would have missed or otherwise forgotten about.
Being that Alex Wesker’s status has not been confirmed to be alive or dead, and that someone with superhuman capabilities has been seen, it’s very likely that this result of the eugenics project will be the next primary antagonist. He will be missed in the series but Wesker was a fantastic villain and served his role well.