Elimination when a player loses all herds, but still has a Chupacabra
From talking (on the phone) with the lovely people at Steve Jackson Games in Austin:

If you still have a die, you're still in the game.

Rolling a Chupacabra essentially means you're safe and can't get kicked out of the game that round. There's no way to "kill" a fellow Chupacabra.

I think that when the game rules say "Even if they haven't attacked" they mean "Even if they haven't had a turn yet".