EDITED: do you mean this
"fiendish" set of rules? I don't know if that's the case but if it is it's a pretty odd choice of monster for the second room you went into almost since it would have a pretty good chance to wipe out most parties. Note that if that template does hold the swarm gets Spell Resistance also meaning that there's little chance the wizard can get them (though worth a try).
So we should sort out whether the swarm has the DR 5/magic thing or not. If they do then you're right that they can by-pass the DR 2/magic of Lazarus. If so we'd have to give Argal the blunt weapon and have him rage and that would be doing enough to kill it after a few rounds assuming the wizard has nothing to hit them with -- I know Todd the sorcerer doesn't. maybe someone should grab that censer from the other room as it would make a blunt weapon too.
Or we could use one of these of course. There are no special rules for swarms but there aught to be.