Hard AI wouldn't be any help at all. It's just as suicidal, and it's just as easily fooled. 1 nightmare AI might be OK'ish in 4v4/5v5 games. Not because it's any less retarded, but the amount of gold it generates offsets its idiocy many fold in smaller games.
Far better to simply disable the dropped player and give a bonus gold/xp% to his team. Or.. You know.. Have GPG make an AI that can actually play the game