I think Katherine, if she dies, will be killed by Elena or Damon. I'd say Caroline should be safe as surely they wouldn't give Tyler the angst of unintentionally killing TWO of his friends (one of whom he'll likely develop romantic feelings for soon) but, well, they didn't think one dead vampire girlfriend was enough for Jeremy. I suspect Elijah will kill Rose, or Klaus will as his "awesome intro." The one I hope Tyler bites and kills is Elijah.