Personally, I think it's stupid to kick or ban a person for running away from a fight in Strategus even if they are the last ones left in a battle. Retreat is a perfectly valid tactic. Hell, I've killed a few people myself just by running away as the last man alive. Usually, this situation almost always occurs when there's a single guy remaining on one team and dozens on the other team. In which case, all you have to do is use superior numbers to trap the single enemy. It's not like the map doesn't have borders. Or you could just offer to duel the last guy one by one to calm him down. The only condition I see that truly provokes a kick is if the last guy is on a roof with no ranged capability and you have no ranged players and no way on the roof.