Acehigh88, Banish happens when they reach your hut. You lose that much Mana and they go back to the start. If you don't have enough to banish them, you lose.
Alex, they're like that for a reason.
Also, I have cornered myself as I can no longer save 50 dinos under the gcurrent rules because I did all the speedruns on insane right away. ;-;
Just to help anyone who is trying to get the Doomed Hero Badge, get whatever buff all skills your characters have and cast them right away. They last for all waves as long as the character doesn't die.