RIP Larry. You'll be missed.
I hope the writers handle this with class and don't prolong it with some manufactured storyline or cliffhanger. The writers on the old Dallas kind of did that when Jim Davis died -- they didn't address it right away, just kept him off-screen, and then had him lost in a helicopter crash. Then they had this search storyline that fell flat because, of course, we all knew Jim Davis had died and wouldn't be found.
If they did a "Who killed JR?" storyline, the only likely suspect at this point would be Cliff. JR had been out of the game for so long that his previous enemies are either long gone or let go whatever animosity they had toward him. And he wasn't back in the game long enough to make any new enemies.