Well well, first post; lets see how it goes... to sum my theroy up I have a few points:
1. The crown of Domminon (Lich King crown) is the source of control over the scourge
2. Ner'zhul, Arthas/Ner'zhul, and Bolivar are all their own intites
3. in the cinamatic : http://www.youtube.com/watch?v=OW02BWFRnkw their is a flash of dark and you can hear Nerzhul make strange noise. the crown of domminon hits the floor and Arthas places it on his head. For me I dont think Arthas would place that crown on his head without influnce from Nerzhul. I think that directly after that noise Arthas and Nerzhul no longer existed and the Lich King had to place the crown on himself again to gain control of the scourge
4. Finally I think that Bolivar as of now is all alone up there and that Nerzhul died with arthas
Just my thoughts, first post so be gentle