so I played a 4v4, and right at the start of the game, 2 of my allies quit out right at the start. we ended up winning anyway, and as I was watching the replay, I noticed that 1 of the 2 allies who quit out actually built quite a few things. I figured that the other ally of ours was actually occasionally going over and building stuff. But really no idea.
I posted the replay here: just remove the .rar from it.