Bob Rae was a Liberal before he was a New Democrat, Stephen Lewis' wife knew he wasn't a real Dipper back in the 80's. Though Rae screwed up as premier he wasn't a hardcore socialist.
As well you say Rae is going to stay on as leader till 2014, even though there is a leadership race set for next April with declared candidates so how is that possible exactly? I doubt the NDP and Liberals will merge before the next election, but it's not that surprising. I don't see why you would think Justin Trudeau would join the Conservatives rather than being either the Liberal leader or a member of the NDP.