My vote is to attack the mutants.

Fire a round at the jeep, they won't know it's coming until its too late. Or, in an effort to save ammo, Drake can get a shot off on the mortar operator. After that, the same plan prevails, stay in the tank, let them come to us. The C4 explosive should take care of a number of them as they approach. Then the heavy gunner can take out a few more. Foresight should be able to take out at least two at that point. Drake will have had another shot off by then. This would leave only three, at the most, when they reach the Bastion proper. At that point they would try to spread out, pincer style. Smokey should be able to take out one at that point. Two left. With another bomb, kirin (I think she's our bomb girl), can lob a grenade at the remaining quad. Their, done. Threat eliminated, minor if any damage to the Bastion. Then we hide the vehicles among the buildings, loot any weapons and ammo, then head out on our way.

Any other ideas?