So we played the 1:1 session and things got a bit nutty.
The PC explored the lower level, survived a few cultist stabbings before they demanded him to open the vault if he was “The One”.
My player came up with some good RP and rolled well enough to crack open this big steel door, the cultists rushed in and then a big battle of the PC “awakening” as many dormant soldiers as he could while this massive oily black starfish creature was pulling the dormant soldiers into its body and blasting them out as animated enemies.
When all was said and done the fort partially collapsed, the big creature broke out into the surface, and the once captured PC now has 58 soldiers who are loyal to him lol. When the party finds him now…he’ll be basically a warlord with a small army!
Haha! Is this how you imagined it would end up? 
It never quite is lol. I think we’re very quickly moving into some world shattering endgame with this campaign (a welcome end tbh).
Amassed forces of fanatical warforged will soon pour out of the Mournland towards the City of Towers and now this small group of warforged soldiers has cropped up on the other side of Sharn. Gonna be a bloodbath
Sounds like fun! Break out your favorite wargame engine of choice, line things up, and knock them down! 
Any recommendations? Guess this is heading towards a session or two of domain level play. I’ve got the Matt Colville doc on my list to read through in more detail to see if it works or if it’s over-engineered for what we’ll do.
What I’ve done in the past is play out the PCs gunning for specific objectives as normal and then using those outcomes to frame how the overall battle/war is going. For example:
The party is under siege in a fortress. They sortie to take out an enemy leader. That causes the battle to shift in their favor. In another sortie, they fail to take out some artillery, that causes the battle to shift against them, etc.
I thought the simplified battle system in Birthright would probably work pretty well for handling some big melees that the players aren’t involved in.
Things are getting a bit wild now. The PC has decided to stay in this broken fort, now has 50 warforged soldiers. Captured a small group of bandits from the nearby road and forced them into fealty, also allowed some remaining cultists to devour the aberrant flesh of the giant creature he slayed, transforming them into a small cadre of horrific evil beasts who occupy the lightless lower level of the fort… he ordered his soldiers to patrol the trade road and tell all that it’s now a safehaven for warforged…all of this within 100 miles of the King’s personal castle.
Now I have to consider what the National Security forces will do when they hear about this “refuge” full of soldiers suddenly cropping up in their backyard. Since these troops were initially commissioned as part of the King’s personal army I would guess some force would show up to claim them…that should go well lol
They have no idea about these developments! Not until they find him. The last thing they knew was their friend got kidnapped by a bounty hunter
With forts imploding and giant creatures rising up out of the ground and then smashed and clockwork soldiers climbing out of holes in the earth, some sort of rumor should be hitting them soon, no? 
Probably after the fort collapsed (it was remote and forgotten) and the travelers on the road were contacted I’m guessing it might take another few hours for those travelers to get to the nearest town. That town however is quite a ways away from where the PC was originally snatched (and where the party will be starting from).
We played out the kidnapped PC’s fate to get an idea what the party might find if they find him. So once we pickup from their timeline, I guess maybe they’d catch some rumors a day later (if they aren’t actively traveling AWAY from the area).
It’s madness, I’m stocking up on red string and corkboards to keep it all straight.
Too far away from some escapee from the fort or fast messenger to show up spewing tales of madness and melee?