An assassin of the school of thought of not allowing oneself to become a leak at any cost, had they had the dentistry, he'd surely have something akin to a cyanide tooth, hell the description of how he died sounded similar to Cyanide.

I think they are perfectly aware of that, what I don't think they realize, is that Yod has splintered, or at least not the extent. however they are in a unique position to cause as much damage as possible, as a medical building, the Directory is an element of the old government that the occupation was likely hoping to leave unmolested, making it the perfect hub for a resurgent Ascendency, we don't know how expansive any tunnel system would be, on one hand unlike the Residence they probably hadn't planned to use it as a staging area, and stone is harder to dig under, but as one of the largest civilian structures in the city proper, it wouldn't surprise me if there were at least tunnels between it, whatever military fortifications there are, what they used as their capital building, and the residence of their leadership. some of those may overlap, but those wouldn't just be for escape, but communication and counter siege. This also means if the occupying leaders are mostly doing the what's usually the logical thing of using the captured fortifications as their base of operations, they are probably in one of the most vulnerable places in the city and don't even realize it. yes they may be aware of the possibility of hidden access points as that's hardly unusual in any fortification, especially given the type of warfare they are familiar with, its almost a given, both the greatest asset and biggest weakness of any castle, what isn't common is for such tunnel systems to be particularly extensive beyond the primary structure they extend from. If they were originally planning what i suspect they were, the saving grace of the allied forces may have been that by using gunpowder to bust the gate, they may have inadvertently disabled the portcullis before it could be used to trap them inside what would be a city of a kill box. What we are seeing is likely an adaptation of such a plan, that the decision to make an assassination attempt forced them to enact early. they probably wanted to wait until more of the occupation had left, to capture any remaining VIPs for ransom killing the rest and capturing any weapons, armor, ships and supplies they could.

and had a good chance at regaining some of it, had they not had a directive to eliminate anyone suspected of Earth origin not under their control. Any advancements would eventually work their way to them, so if they waited until most of the occupation left, they could have had most of their cake and eat it too,

indeed, the convention, while sensible particularly with so many different allied forces, of waiting till dawn gives the Ascendancy time to set up barriers, i doubt they'll set much ablaze, too obvious and ruins much they might wish to use to follow up, they might try for some of ships but those are being well protected, a bigger potential issue depending on the extent of the tunnel system, is any powder they may still have, possibly may have even been producing secretly during the occupation, (charcoal and saltpeter are likely traded freely as fuel and fertilizer, sulfur would be less common, but proportionally you don't need much) if they connect to the sewer system, even if they don't have a lot of it or even any guns, they could place it underneath several key intersections creating bottlenecks, actually if they are clever enough, they might use the thunderstorm to disguise the noise. if they are smart, they wouldn't block anything outright, as then they'd just clear the obstacles, bridging or otherwise, creating a winding path of least resistance spreads out and fatigues any attacking forces