Looking at the possibilitys, i feel that Sylar may be one of few who can stop Adam Monroe from living.

Once he gets his powers back, and he knows of Adam's existence, he will fancy a shot at immortality.

If he takes Adam's brain and does his magic(turning his power into his own), then we have the worst possible villain of all time, a psychopath merged with pure invinciblity.

Another character who may be able to finish him off is Maya. She isn't exactly wounding him when she uses her "internal murder" power. It will be interesting to se if he recovers from that.

Suggestions?