As an Alien, you regenerate in this game.
For me, that's enough to offset the fact that the headbite isn't a viable combat tool this time around.
Not that it needs to be - in AvP2, your claw and tail attacks were so weak that headbiting was an excellent way to get lots of quick kills. In AvP1, your attacks were murderous hurricanes of wrath and killed anything that wasn't a Predator in one hit. Unless you used the tail attack, which downed Predators instantly.