As others have noted already I can't help but wonder if Rem would really die by taking revenge on Light if he were to kill Misa. I was under the impression that this would only happen if a shinigami prolonged someone's life expectancy by preventing the person's death. Which wouldn't be the case here, if she killed Light after Misa was already dead it would only be revenge, not helping her. Seems like the show messed up here to be honest...
Also not sure how Misa would kill any girl that Light would go out with, if she doesn't have her death note. Would she actually go do it the oldfashion way?
One other thing I was thinking about just now... Misa traded half of her remaining life span to get the shinigami eyes, but didn't she get Jealous' lifespan added to hers when he prevented her death? Then perhaps half of her remaining life span wasn't that bad, who knows how much lifespan got added to hers already. Just imagine if Jealous had a few hundreds of years in reserve... [edit: I see it was mentioned in ep12 discussion too, guess I didn't read that one properly]