No way would RR show up on this show.
Bringing in Karen would be cool, cause like someone said earlier she could be brought in as someone who might be able to help cure Krista, even though I don't think a cure would work.
Karen was able to cure herself, because she didn't turn all the way yet, Krista has been a vampire now for what? 6 weeks now? She has turned someone already so I don't know if a cure would be helpful.
All though Karen would be usefull in the liquid Blade took from the pregent woman he saved.