i have yet to read the 4th book, but i am pretty sure i know i little bit of how it ends. But with the fact that i have only read up to the 3rd, my opion is that i think that as much as Rose at the end of the third wants to kill Dimitri, i dont think she will be able to ever do that. She is so in love with him i think she would do anything to have him with her forever, even if that means she would turn herself. Please no one think that i am saying that i want Rose to turn herself and leave behind Lissa, because that is far from what i want this to end like.
Rose and Dimitri's forbidden love was one of the main reasons i fell in love with this series. But as much as i would love this is have a happy ending for the two of them i think that it will in some way have a crazy, freaky, unexpected twist to a happy ending.