I think NBC is finally sick of anything Heores & wants it gone fast.
They better wait till they see how their new fall lineup does.
Heroes at least has buzz and international pull. Their new lineup is far too generic to do well in either area. My prediction is yet another NBC bloodbath, with a few of them hanging on by their fingernails with a very modest audience good for maybe two seasons if they're lucky. There aren't any shows in their fall lineup that look like they have breakout-hit potential at all. NBC's strategy is mere survival, not hitting for the fences.
In the body-wars, my money's still on Nathan, since now that they have Robert Knepper to be their resident kick-ass villain, Sylar's value will plummet accordingly, and to permanently lose his identity to Nathan would be a suitably ironic end for the character.
In fact, here's how I envision it happening: Peter finds out the truth about Nathan, and after spending a few episodes throwing fits/trying to kill Nathan/yelling at Matt, Noah and Angela, he finally settles down and realizes that this new Nathan, tho not his brother, is a decent guy. Little by little, they become friends. Some angst ensues as it becomes obvious that Nathan is in danger of losing control to Sylar.
Then Nathan absorbs the power of being able to split in two, which results in a physical split between Nathan and Sylar. Nathan may do this
in order to split Sylar off. That can lead to the final showdown between Peter and Sylar that we all expect, which now is not only to kill Sylar but also to save the Nathan persona (let's say there's a ticking-clock aspect to the split thing; it can only endure for a certain peroid of time, after which they merge and the assumption is, Sylar is now the dominant persona).
That should carry us thru S4 with the big battle the season finale, and if they develop Knepper well and hang onto the guy, he can take over Sylar's function in the story, assuming there is even going to be an S5. If there isn't, oh well, at least they finally will have resolved the Sylar story. In fact, it would be for the best if there isn't an S5, so that there will be no temptation to do the obvious - oh no, Sylar isn't really gone after all...
If you die, it just means there's an even greater chance of you having more appearances than ever before! Darla, anyone? She died 4 times and still came back as a ghost (not to mention the glut of flashbacks)! Angel? Spike? Buffy? Lilah? Holland? The fact that we've seen Wesley, Cordy, Warren, Tara, Jonathan and even freakin' Catherine Madison (I wonder if she's still in her trophy buried in the Hellmouth) appear in recent comics? The First was just an excuse to bring back a parade of the dead and the living dead. 
Characters like the Master and the Mayor were popping up years after they were dead. Hell, Kakistos just got a comic outing.
