OK, here's what happened:
Idiot the Thief-Mage fails to grok that this magical trap they've detected is higher level than she can deal with and blithely goes about setting it off. It's a Prismatic Spray. (It's worth noting that before starting this adventure the group learned that there were powerful traps and the players had carefully plotted how their characters will avoid traps by using short-range translocation magic.)
Not one, not two, but THREE of the party manage to roll a 7 on their random Prismatic Spray effect which is "Get sent to another Plane of Existence". Two of them make their saves (whew!) but not the third. The one that failed, though, is the NPC whom the characters have just met and whom they have no reason to like overmuch. In fact, she's been something of a dick to them because her lover is in trouble offstage and she gets cranky when nervous.
Whew, says I the GM. At least it wasn't a party member they'll want to... wait, what's that? Noble Soul the Cleric is talking the party into going to another plane to rescue the NPC? Ah, not so much talking them into it as joining the enthusiastic chorus. What the... Oh, and Noble Soul has an empty 5th level spell slot, which happens to be the right level for Plane Shift. And the psion has a cross-planar means of communication so they can figure out where said lost NPC is. And now Noble Soul is making prayers to his god for divine intervention here because he has no hope otherwise of getting the tuning forks he's going to need. Well, that's no problem, he only has an 11% chance of that working... and he rolls an 06.
(Aside, I should note that the players are alternating between gales of laughter at the situation/GM's discomfort, and fairly earnest role-play. They are totally into this.)
So game gets called until next session while the GM scrambles to figure out how to have an extra-planar adventure that won't kill off the entire group. Because in addition to the special effects and budget committee I'm also the entertainment committee. Yes, I could have fudged any of those die rolls. But that sort of deus ex machina stuff always rubbed me the wrong way when I was a player so I try hard not to do it as GM.
And I carefully set aside the thick stack of paper representing hours of prep work and figure I'll get cozy with the Manual of the Planes for a while.