Even though the game tried to imply that Wesker was intending to bring Umbrella back all he really did was join up with a new company in RE5 (Tricell) and try to commit world-wide genocide with his new Uroboros Virus (which makes me question why he needed the Plagas parasite in the first place or even the G virus and T Veronica virus). He clearly didn't even give a crap about Tricell he was just using them for his own agenda (which obviously had nothing to do with bringing Umbrella back).
I just don't understand why the developers had to kill off Umbrella or what Wesker's "plans" had to do at all with supposedly reviving the evil company. That would be like if Ganon was suddenly killed forever in Legend of Zelda and they completely replaced him with some new villain nobody gave a crap about who constantly blabbers about wanting to revive Ganon but never actually does.