You can set allied victory with any player (It should work with comps), so basically, if the players all are allies except for the computer, you could set the comp to allied victory.
Trigger |
Players: |
¤ Player to ally with computer |
Conditions: |
¤ Player to ally with comp has only one opponent (the computer) |
Actions: |
¤ Set Alliance Status to Allied Victory for Computer Player |
This trigger basically checks if you only have the computer player as enemy and then it sets it to allied victory. If the computer player dies, I don't think it'll do anything weird.
You could just end the scenario in victory also. Be warned that this won't work properly if the computer player can die.