They can retcon away the poof problem because Sylar actually has two full people bopping around in him so both are real. Or something. Plus shapeshifting makes them uh more solid!

This is the last show where we need to be sticklers about logic.
Here's how it goes down:
1. Peter finds out about Eli and takes his power.
2. Peter enlists Claire's and Matt's help in his hairbrained scheme.
3. Peter confronts Sylar, intending to lose the fight (not too hard to arrange).
4. Sylar opens Peter's skull and takes the multiplying power.
5. While Sylar is playing with his new power and splitting off selves, Claire grabs Peter's hand before he totally buys it and he gloms her healing power.
6. Sylar is distracted realizing Peter is still alive.
7. Matt takes advantage of this to push "all" of Nathan into one body and "all" of Sylar into another (do not think too hard or logically about this!)
8. Thus we have Nathan and Sylar fully returned as independent characters.
On the ratings front, a bit of an uptick for
Heroes: 5.90 million; A18-49: 2.5/ 6. The demo numbers have been stable around that mark for most of this season. That combined with the utter failure that is NBC might just get it another season (whether they another season worth doing is another thing entirely).
Sylar should be able to detect the Haitian...as quiet as he is, Sylar has super hearing, and could then know if the Haitian (or somebody) is around, and therefore keep out of range.
I think super hearing was one of the powers he lost in S2 for no particularly good reason since he retained the TK. I can't remember any time since S1 when he's used that power. Unless Sylar knows who Rene is (have they ever met?) he'd probably figure he was just another one of Peter's dopey friends and/or co-workers. If they were smart, Rene should dress up as a paramedic.
Sylar is not the cautious type. He attacked Peter blithely knowing that he's got
some power. What if Peter had been smart and glommed Matt's mind control power (assuming Sylar hasn't retained that, and is therefore immune) or some power Sylar doesn't even know about. Peter could have a power that kills anyone who touches him for all Sylar knows.