In campaign mode, in some scenarios AI shouldn’t resign.
Take the second scenario of the Greek campaign: you have to capture some ruins and build some towers. But you have to pass trough the enemy base, so you have to strike a serious blow to accomplish the objectives. But if the AI resigns, the whole scenario loses the purpose and becomes another deathmatch.
So my proposal is that, in the scenarios that you have some kind of objective more than defeat X enemy, AI should be programmed to never resign. Elimination victory should be allowed, of course, if for some reason the player is unable to accomplish the goals (in the same scenario of before, for example, you run out of stone for building the towers, so you can still win by killing every unit and building)