They tried to convince those of us on 'origin' servers to transfer willingly to 'destination' servers ahead of the merge, though, which strongly implied those servers were the ones sticking around. Otherwise, why bother trying to encourage folks to move to one of the destination servers of their own free will ahead of the crunch?
I was around then and I remember well that I expected merging of servers (even when BW was going with transfer they had their CS reps on the forums tell people there is no merging) with the free transfers. If memory serves when it came to the consolidation of servers they used a few different variables but it usually had to do with time. How long the character existed, how much time it has been played, etc.