Ya edited my post, though it doesn't say how he died though. Luke could have just passed away peacefully or some such nonsense by something. Vague deaths for all 3 characters, would be the best bet to go about them. Because no one is going to like the deaths, if they are described in detail. I mean look at Chewie, took a moon to kill him yet people don't like that he was killed.
I know what you mean about Chewie. Salvatore did a great job sending the ol' Wook out in the ultimate blaze of glory.
It all depends on how George worded the orders, though. If he said "Luke, Leia, and Han can't die", then that's that. If he said "Luke, Leia, and Han can't be killed", then MAYBE they can loophole it to make them die of natural causes.