My friend and I tried skirmish mode last night vs AI. We wanted to team up for our first match and figure out the game. The two of us managed to defeat the enemy AI gangs, but after that the game just kept going, as we ended our turn over and over.
I assume it was because only one player was allowed to win, but since we were on a team we weren't able to attack each other. The game only ended when one of us forfeited, and therefore injured our gang and lost half the equipment.