Giantitp had an interesting 2-page argument about suffocating in force cages (not related to OotS, back in May):
http://www.giantitp.com/forums/showsinglepost.php?p=22018966&postcount=56I've linked to basically the end of the thread because it's by far the best part. Though the post is about resilient sphere... A force cage definitely will suffocate the people inside, unless the air is magically replenished or selectively allowed in (I don't the argument was conclusive, so GM call IMO).
Yeah, this still seems like a non issue. Most of the vampires are probably trivial spawn, the heroes have whatever set up time they need, sure Elfboy can't come out blasting but he can set up whatever other spells will be useful and if the heroes can't beat this group of vampires readied actions with their own readied actions they're probably hopeless anyway.
Ehh, the vampire spawn template is pretty heavy.
http://www.d20srd.org/srd/monsters/vampire.htm (scroll down to spawn)
The dominate is only 5th level instead of 12th, but there are a lot of them. I'm pretty sure Durkula's a spawn, and it was able to dominate Belkar with apparent ease. Belkar obviously has low WIS for will saves, but is Elan that much better? Or V, who sold their soul?
Besides that, such a large group of vampires is very dangerous in melee. If they hit, they deal negative levels without save. If they grapple and pin they start doing CON damage every round, and large groups are exponentially good at maintaining grapples. Think like a zombie apocalypse.
Their HD also switched to D12 (I think) and they definitely heal 2 damage every round, so the wounded can fall back to recover. There are lots of them.
If Varsuvius was killed, wouldn't the force cage be dropped anyway?
It doesn't require concentration, so I'm almost positive the answer is no. Particularly since the comic says V needs to manually dismiss it.