mercer dies badly. This is pretty much a question of how long he can annoy the hulk before his ass gets punched to the moon. A far closer fight would be mercer vs carnage or venom.
You know? This is Comic Alex, not the video game one. The Video game one(Prototype), bullets hurt him. If Comic Book Alex, Normal Bullets don't hurt him and maybe Comic Book Alex is the immortal One...
bullets hurting him is only a game mechanic. All throughout the game he took machine gun fire, tank shots, super soldiers, and infected elites. He was powerful, but it was made very clear that if he took enough physical damage, he could be beaten if not killed (as demonstrated in the final fight in prototype 2). Mercer isn't nearly powerful enough to inflict any lasting damage on banner.