The game always tells how much the Ironheads are a threat to Foundry's existence, but you never actually see them attacking Foundry or any of it's soldiers, I think it would be kind of cool if under certain circumstances or elapsed time you can defend Foundry from a huge Ironhead assault, with timed waves like in the Praetorian warehouse quest, you can accept it for a lot of experiencie and coins, or you can ignore it and Foundry has a chance to be completely wiped out and instead be populated by raiders.
Imagine it, you're calmly traveling around Underrail in train, you get off the train station on Foundry, and the moment you enter the zone, combat starts, but you're not fighting, instead you can hear gunshots and explosions nearby, it's a small squad of Ironheads fighting the Foundry guard, you can either help the guards or let the battle play out. Then you can talk to the chief and have a chance to accept the quest to defend Foundry for huge rewards, if you accept you will have to stand at Foundry's entrance with a dozen of Foundry guard, then after a brief moment, dozens and dozens of Ironheads waves attack Foundry, having to hold the line.
The waves would be timed, so you could get a solid minute of between ever increasing waves, so you can recharge items, heal, stabilize yourself, etc.
If you run into Foundry if you're getting overrun, you now have to defend Foundry on the last line of defense, on top of the few guardsmen remaining, half of Foundry residents would defend it with any weapons they have, however they would be weak combatants, if you leave Foundry during the quest, everyone gets wiped out, and all traders die, including Leonie. Chief Banner could also be there, defending.
If you successfully defend Foundry, you could get a lot of coins, exp, cheaper traders and more importantly, fame and bragging rights.
Would also be a good chance to demostrate the cowardice of Foundry's Mayor. Also if you successfully defend Foundry, the Ironheads base would be half populated, reeling from a massive failed assault.
This quest could trigger if you take way too much time without killing Balor or if you reach a certain treshold in the game story, for example reaching Institute of Tchort without killing Balor, or certain amount of in game hours. Tho I suggest this quest to be Dominating only.
This quest would be a relatively late game quest, so the player is well set for the whole combat.
To some extend this quest could also be applied to Rail Crossing, tho in a much minor scale.
