I think we are in fact going to encounter 1st counterparts of people on the source. Yes, things developed differently in the 10,000 years since Hydaelyn split, but in all that time, out of all the dice throws that can occur in that time leading up to the present day, at least some of those dice throws had to land the same as they did on the source.

I think the theme will be that people are the end result of their life experiences and don't really have fates that are set in stone. So you will see the same people who ended up radically different than they did on the source and in that way, they are not the same person.