He died. His corpse was used as a source of t-Veronica by Umbrella's rival company, then he was likely disposed of. He had no chance of coming back. Only the G-Virus could revive the dead at that point, and the result was only a G-Zombie. That's the significance of Wesker's line about Claire maybe seeing him again, it's a cruel joke to suggest she'll meet him again as a mindless monster.
Thanks for the clarification. I would really like to see Rebecca in another main game.