Lol, if he didn't turn on Auto-Gameover, I don't think that will help much. xD
@mcLeod: The Auto-Gameover option was intended so that you can either turn it on and have your game end when all actors are dead or turn it off and handle a gameover with events. I didn't expect somebody would allow the player to walk around with dead actors so it's pretty much unexpected behavior.
I just checked the code and yes, when an actor is dead, the AI will not use any actions, but if the actor is controlled by the player, the player can still press a button to activate an action. And I actually would want to leave it at that.
But there is a way to avoid that. You can simply have a parallel process common event running that disables the attack, skill and item buttons when a gameover should occur and enable them when not.