Well, if you use the PT as a body of reference, he might have caught the blast in his hand, or mouth, and spit/thrown it away. Or, he might have teleported, or CGI flipped out of the way. Really, the possibilities are endless.

But in all seriousness, that would have been an odd plot device. I wonder if Yoda would have simply taught him as a Force Ghost...or maybe Luke just gives up (his x-wing is just about submerged) so he lives on Dagobah for the rest of his life. Man, I dont think Empire would be my favorite if that happened

P.S. I was looking at this chocolate bar I bought, its from a company called Dagobah, and on the back it says that Dagobah is Greek for "temple of the Gods" or something to that effect...I thought that was neat.