I doubt the writers even know who killed Nathan yet. We all know this show is made up on the spot.
It sure feels that way, especially this season, which has been on whole, pretty terrible. Anyone who thinks it's better than season 1 must be deluding themselves.
Anyway, here's some stuff that was supposed to be on Heroes, but was dropped for one reason or another:
1) Kristen Bell was originally supposed to be in 8 episodes and then killed off but due to fan support they are keeping her around for a bit longer
2) Elle was setup as a Bob's step daughter and the daughter of Meredith which in turn would have been Claire's SISTER but they dropped it due to lack of storylline and plot holes.
3) Stephen Tobolowsky (BOB) also had a slightly different story, he was supposed to be more evil then he is now and even recruited his SON WEST to make Claire turn against her father this was dropped early in Volume 2 for "various reasons".
On an unrelated note, I have to say that this use of blood for curing everything is going to lead the writers down into a slippery slope. It's just too convenient as a plot device as it's just a reset button for them and it will encourage sloppy writing (not that it can get any worse at this point...). Anyway, to further nitpick about Heroes, Claire's and Adam's blood type must be O, or else they wouldn't be able to donate it to everyone. Also, am I just making this up, or didn't Mohinder say his blood type was AB earlier?? (But that doesn't make sense either since he's been using his blood on other people, and it's unlikely that there are so many AB genotypes around).