I don't actually buy that person's rationale, mostly because I tend to see a timeline and future travel as a direct representative of the past, rather than an alternate reality with the 'past that was', as it were.

I'm finding it hard to believe that Sylar ever was the bomb, where it makes perfect sense to me that it was Peter and Nathan covered it up, and this fits into my teeny pet theory where Sylar doesn't actually know Nathan has powers and kills him for both revenge and political power which would be kind of a departure for him.

I worked out where I was going wrong in the timeline with my paradoxes anyway, I was working off the (stupid because I knew it was false) basis that Future!Hiro was correct that Sylar was the bomb. Since, as we're told by both Peter and Sylar, Peter is the bomb it makes no difference to the timeline whether the cheerleader is saved or not because it is not stopping Sylar that will stop the bomb.