if he killed her, she'd regenerate anyways, right?

Her brain is the source of her regeneration. Since Sylar kills heroes by taking their brains, I think Claire (along with all the other Heroes that Sylar knows) is still in serious danger.

Yeah, Sylar would have decapitated her before she had a chance to regenerate.

My guess it would have been awfully hard for her to regenerate without her brain.

Yes, she was in danger and she still is in danger.

I think in order for her to spontaneously heal, her body parts have to be in the appropriate position to heal. Like with the whole Brodie incident. She couldn't come back to life until that small stick thing was pulled out from her spinal cord (or whatever). Also, she had to push her own ribcage back together before it'd heal up too. That and whenever she has broken bones with the limb in an obviously weird position, she has to put them back in their normal place (ewwww!) before they heal.

Anyhow, I think that if anyone TOOK any part of her, she couldn't heal up. If anything, someone taking her brain would probably be the end.

I think we will learn a lot about everyone's power in the next couple of episodes...

I agree partly that "she has to put them back in their normal place (ewwww!) before they heal." What about the garbage disposal incident. There were fingers missing and they seemed to work themselves back. We'll learn a lot soon!