Well, jcorvette, from long experience I find that a sarcastic response just doesn't work well. Believers are going to believe it was their god at work no matter what you say or do.
If a good thing happens, that's just proof to them that their god is at work.
If a bad thing happens, it gets one of three responses:
a) it was their god's will (these are the true believers)
b) the lord works in mysterious ways, his wonders to perform
c) god never wills evil, but because we are fallen into sin, evil had dominion over us
Being civil is never a bad thing, and foregoing a sarcastic response is being civil. Or you can ignore them. Or, if you have to say something to keep your head from exploding, just stick with something reasonable like "A word of thanks for their doctors' skill would be warranted as well."
But that's just my opinion.