I think there was a Claudia in this world, because she was not affected by the loop. So, that's why there was a Regina. We just didn't see her at the end.
The characters that can't exist in this world are the ones affected by the loop: Jonas and all his versions, the Nielsen family (Ulrich and the children), Charlotte and her daughters. It's funny, because when they explained what they were going to do, I started calculating who couldn't exist in the original world and I thought we'd see Peter married to Katharina at the end. It felt good to be right.
I may not have understood a lot of what was going on, but I found the end really satisfactory, especually since I didn't expect them to be able to explain it all in a way that made sense.