The fact that the first two deaths were guys makes me think that one of the girls will be next. And the fact that Kaylee and Simon got their happy ending (at the end of Serenity) leaves me a bit less convinced that Mal and Inara will get theirs.

Inara because it was revealed that she had a terminal illness. I imagine her relationship with Mal deepening before her death but they'll definitely never get a happily-ever-after. And I think that's part of why she's always held back- she knows there's no future for her.

I honestly don't think anyone would've died. I'm pretty sure when they made Serenity the movie, they knew the show was ending.

^I agree that they definitely knew that the show was over and that Serenity was meant to be closure, but there surely would have been some character deaths eventually. Has Joss Whedon done anything without killing characters off?