If it is going to go multiplat, fine.
Just make it a Timed Exclusive. Release the two versions when they are done. I am sure MS will help with advertising the Xbox release again, so why not? (and this is not a crack at MS, it is the truth)
It has happened to countless games this gen, why not another one?
Until they announce anything, this is all just speculation. I do think, however, that the above will make the wound sting less (the fact that SE could potentially lie to the entire PS3 fanbase)