Of course, the convention is a formality, so it could just turn into a huge conference call and be done in one day. Then everybody could go to the Minnesota State Fair and eat cheese curds and lutefisk.
But I don't think the media would have accepted the idea of canceling the Sermon from the top of Mount Hubris if the storm had come in a week earlier. After all, humanity has not seen that scale of political event since Nuremberg in the 1930's, and the media would have felt cheated if it had been interrupted in any way.
What speech?
I think the best thing the Republicans can do is assemble a quorum, get through the business side of the convention by a voice vote, nominate John and Sara by acclamation, and say “Okay, let’s get to work raising money for the states hit by Gustav.” They can keep the convention open for 4 days and still get the message through.
Don’t cancel.
Instead, have a WORKING CONVENTION in which people from Louisiana, Texas, etc - or from FEMA - are shuttled back and forth as necessary so they can do what they have to do.
Delegates from Louisiana, Texas could vote from “home” if necessary, and John McCain and Sarah Palin could do several remotes from the hurricane area.
This hurricane, in fact, could show the country how dedicated and professional the team of McCain/Palin will be in the White House.
A pared-back, lightly attended, semi-ignored, GOP convention prevents the DBM from tying McCain to the "reviled" Bush administration as tightly as they'd like to.
Nya-nya-nya-nya-nya-nya!