I'm pretty sure he'll be back for at least a couple episodes (kind of like Lena) because I think he is also another show (from what I remember). But, last we saw he was alive, so we'll probably get to see him AT LEAST once!! (Love Weiss!)
i just read an interview with him and he said he is doing a couple films this summer before returning to alias for next season. i think i read it on this site too. it seemed pretty clear that he'd be back next season. so i'm not worrying on that one.
Greg Grunberg has been bumped up to a regular cast member this season rather then just a recurring role. From what I have read, he will be in just about every episode. He told Kristin from eonline.com that he is in a lot of the first episode. So yay!!! Lots and lots of Weiss!!!
<Insert shamless plug..hee hee> Any Weiss fans should feel free to check out my Weiss group called The Yo-Yo Ho's. The link is in my signature.