I honestly think Emily and Victoria being the Two Graves would be so tragically fitting, but ABC/Revenge writers would NEVER kill off the main protagonist in this series. It's just not happening--Sunil called the finale "bittersweet" so I'm sure there will be some sadness/deaths but it will likely be Emily being alive and a more minor character dying, thus making it bittersweet.
Honestly, that preview of the Emily/Victoria showdown kind of dampened my hype a bit. I'm hoping other parts of their conversation are better or the lead up is incredibly good because for a show that centered on their quips back and forth I really just want them to have at it
My bet is Victoria and David being the two graves (David being one is such a cop out though...) and I do think we will see Nolan and that guy together again. I don't think they just brought him into the story to make Nolan forever miserable.