Apparently the actor that plays him (also got killed off of Greys Anatomy this week, and Weeds which is a US show) is really busy and has got his work schedule filled for the next 6 months or so.
I think the character has gone to hell, but might make an appearance later on in the series, but they're not 100% sure.
I want to know what's going on with Sam, and what John whispered to Dean that had him looking so shocked (I'm sure it was the 'truth' about Sam).
Maybe there's a big fight coming that all the children like Sam are going to be involved in??