Update: So he is technically killable. The animation where the soldier stabs him plays, but then he takes it like it's nothing and continues trying to rout.

Another update: So he died after the battle. Shame you can't actually kill him during it,

It is not impossible. It's hard to kill him but he dies in the end. After attacking him with the whole army it seemed more effective to attack him alone with the general and it worked. Hannibal is dead.

unfortunately the HP of the general is hardcoded, and in AE the unit damage is much smaller than in vanilla Attila. As such killing generals is somewhat difficult, as mentioned using one unit seems to be a better option.

i killed him the first battle

just pretend you are john connor and you fight the t-800