Seems comedian Seth Rogen used comedic licence when recalling his conversation with Lucas about 2012's doomsday. Never! Lucas' rep did say however that George is "an adamant believer that the world is flat, that Stonehenge was built by aliens..."
...and that the sun revolves around the Earth". His Lucasfilm representative Lynn Hale told Wired.com that "these are among the many subjects he commonly discusses at length with Elvis, who he's going to digitally insert into Indy 5 along with a roster of famous dead actors".
Hale may've been joking, but word on the Tatooine street is that Lucas is already buying up the film rights for deceased actors, so he can digitally insert them in his movies. Having seen Elvis turning tricks in Wild In The Country, it's not completely crazy to imagine him propping up the cantina in Star Wars: Return of the Peanut Butter and Banana Sandwich.
Nonetheless, Rogen's definitely going to get in trouble for this - and if he thinks he's in for a chance of hitching a ride on the Millennium Falcon when the world really does end, fat chance - according to Hale, "George and Steven are taking Chris Rock with them on the Millennium Falcon!" [Wired]