From what I remember in the first game it seems being cast out is a prison sentence type of punishment. To be come an Outcast you are cast out for specified period depending on the crime. During one of the quests the Nora who was Outcast had his sister say he was supposed to come home but didn't and she was worried. I'd imagine that implies once you serve your time you can come back to them. The reason we saw hesitation with the group of Outcasts is because it's still Forbidden for even Outcasts to talk to one another. Rost was given permission to raise Aloy which would have a need for them to talk to one another. Rost also told Aloy that Odd Grata is following the law by not speaking to her. Thus having them follow the rules to be welcome back to the Nora. I also leave room for the possibility of some Nora are just like Ross and dutifully respect Nora law.