Firstly, to the Moderators - if you deem it necessary to move this into the Season 4 Speculations thread, then you may do so (you'll not get no argument from me). I simply felt that this topic would receive a stronger point alone. That opinion though, is your decision. If you do combine this thread, could you please remove this paragraph.
We know that season four is going to present us with a death, and the death is going to be a male character, that has been with us since season one. I'd like to look at that in a little more detail, and would like to share my thoughts. Out of all the main characters we have with us at the moment, in my opinion, there are only certain ones that this death could apply too.
Hiro: He has a Brain Tumor, which at present, nobody seems to be able to heal. Unless he actually makes it back to the present, and to Peter some time soon, Peter will end up acquiring a new power, and as such, wont be able to heal Hiro any longer. This would then lead to Hiro dying.
Matt: We know he has problems at home now, with Sylar. Sylar wants his body back. In order for that to happen, Matt must actually be next to Sylar's body. The minute Sylar is transfered back, is he really going to just let Matt walk away?
Noah: His story lines seem to be a bit dull at the moment, though this could change, as there was mention that he was after the carnival lot. Should this be the case, his character could get a lot more interesting. I do believe though, that I read the actor did want to move on at the end of season three, so it is possible he is the one to go.
Mohinder: This would all depend upon the timeline. At present, we know that Samuel has killed Mohinder, yet he has asked Hiro to take back that 'mistake'. As such, Mohinder wouldn't be dead any longer. Saying that, if at the end of this season, everything Hiro does is somehow undone (saving Charlie, getting Ando and his sister together, arriving at the carnival etc) then Mohinder will again be dead, at the hands of Samuel.
I've left Peter out for a very specific reason, that being, I think there needs to be a Petreli left in the show. Some would say that Peter has always been more of a main character than Nathan, whatever the case, I don't think they'll be letting Peter go anytime soon.
I don't think they're going to kill off Ando either, I don't think his death would warrant such a huge problem (for lack of a better word). I don't see people that bothered about his death. His character, as of late, hasn't really had much to offer. Same goes for Sylar, in the sense that I doubt they'll kill him off. He is, and always will be, the main villain. There is no escaping that, unless, Hiro's latest quest into the past has changed him.....
There is also the news that Nathan's character is properly gone, and that Adrian P is leaving the show, it is still under speculation I think, as to whether this is the death the producers were speaking of. In one light, his character was already killed off in season three, but in a different light, his 'conciseness' is still live and kicking. In Heroes, is ones conciseness classed as a 'character'?