This is a classic siege situation. They've effectively used magic to circumvallate and countervallate Karak Vlag so they can invest it.
The classic solutions to a siege are:
- Reduce or assault the countervallations to destroy the attackers in battle
- Reduce or assault the countervallations to distract the attackers where the defenders can sally and break the circumvallation
- Lay siege to the attackers, who as a maneuver force will have almost necessarily been less-well-prepared for a siege than the defenders.
I'm certainly leaning toward disrupting the flow of magic, which will conveniently do
all of these at once. The attackers in Karak Vlag are dependent on the magic to survive and have only a few days of "supply". Furthermore, the attackers are heavily dependent on their "fortifications" to keep the dwarves of Karak Vlag under control: I strongly suspect that Karak Vlag's defenders are substantially stronger than its attackers, militarily speaking, and the demons are just there to keep them from getting out to the boundary where they can work on dismissing the effect. I suspect that disrupting the ritual will therefore allow Karak Vlag's defenders to sally - or outright evacuate the Karak with all their stuff - and potentially even smash the demons on their own.
Either way, I'm leaning toward clogging the next waystone upstream. That'll take the initiative and force the Chaos forces inside Vlag to respond. Once we know how they've responded - likely by sallying to assault the Waystone - we can fight them. If we're really ballsy we could leave Asarnil and Deathfang outside to keep them from unclogging the Waystone while we assault the investing forces.
The clog may not be safe to leave in place for, like, months, but we don't need it to last that long. At worst, we might be able to get Cyrston (or even reinforcements from the Colleges!) up to set up a big ritual to "use up" the flow so Karak Vlag's flow doesn't resume while we unclog, clean, and re-clog it.
