dervish,
Just how did Salmond get "blown out of the water"? He went from well behind in the original polls to within a hairs breath of winning the referendum. I can't see Jim Murphy being in a "powerful position", leader of Labour in Scotland with just a handful of westminster MPs and in opposition in the Scottish Parliament.
The people co-operating will be Salmond and Milliband if your scenario comes to pass, which I believe it will. Murphy will be an irrelevance.