Hannibal Chew shows up in just one scene. While fiddling around in his freezing cold lab, Chew is interrupted by Roy and Leon, who tear off his protective coat. Freezing and at risk of death, he tells them that he's just a genetic designer who creates eyes for replicants—something Roy and Leon know, since he designed their eyes. They force him to tell them who might be able to help in their quest to extend their lifespans, and Hannibal mentions J. F. Sebastian as someone who can take them to see Dr. Tyrell.
We don't get to learn about his final fate—although there was supposedly an un-filmed scene in the original screenplay, in which Hannibal's frozen corpse was discovered, shattered into pieces (source).
Hannibal doesn't really seem to think too much about what he's doing—he's just making eyes, right? Just following orders? Yeah, well, that's a bit of a problem, since the whole system is kind of corrupt. Hannibal may just be making eyes, but he's making eyes for what are essentially slaves.
That's the big picture, and it's not pretty.