Okay I don't know if this relevant at all or not, but as I was re-reading chapter 10 (when Yuno first meets Yukki's mother), Yuno mentions that Yukki will come to love her eventually, and that they will be 'bound together' in July 28th, the same day that, according to MuruMuru, is to be The End of the World.
Interesting. Gives me the impression that the world's destruction cannot be reversed and on their last living days Yukki and Yuno make out just for the heck of it.