If Peter could regenerate the Haitians memory wipe thanks to Adams (and Claires?) power, maybe Adam is even better at it, and thus is totally immune to the Haitians power.
That might explain why it was impossible to kill him, even with the Haitians help. (Though I think it is still more likely that they kept him around because there was still so much to be found out about his powers).
Vocenoctum said:
Given the symbol, I'd almost hope it's something divine or something, rather than a simple "we're mutants" thing. Especially given how none of the families seem to share powers.
In the Heroes timeline, the symbol appeared together with Adam - it was his chosen symbol for his Kensei identity. Maybe he _really_ is "Adam" for the purpose of superpowered heroes.
We don't know yet how many heroes actually exist, but is it possible that they could all have the same ancestor? (Very fruitful then, this Adam guy

)
What if at some point regeneration can be trained to degeneration (no cross chops folks). What if adam can break down cells as well as he can repair them. We've seen all the other powers get exponentially better.
What if it can be used to _mutate_? Maybe Adam found a way to use his regeneration power to mutate other people. (Which cuts down the required scope of his libido

)
Maybe the strange sequence in the DNA that looks like the "Godsend" symbol is actually Adams manipulation?
Maybe I am getting a bit to hung up on my idea that Adam might be the original Hero, but I really like the theory.
Maybe the superheroes are like a Cancer on the scale of humanity instead of a single human. The Hero Trait starts off as a single cell that is slightly mutated. The cell multiplies itself (Adams first children), and begins to spread through the world (adam and his children wandering the world). Instead of damaging the surrounding cells/organs, this Cancer transforms them (maybe some cancers can do that? I don't think that's normal, though), which is the next step. Now, the cancer is everywhere in the system, and the only cure (the virus) is like a chemo therapy - yes, it affects the cancer most, but the rest of the body doesn't take well to it, either. And if you're unlucky enough, it kills you (the Ashanti virus affects all humans)...