I think this kid is definately going to return. She'll be older, and therefore more dangerous, and out for revenge. Plus, she'll bring all that PTSD back for Michonne. I don't think you let the kid live to never bring them back, it's too powerful of a story technique. I think we will see her before the end of season 10 for sure, and she will help in either sending Michonne away, or tying up her arc before she leaves. I'm excited for where it goes.
For anyone whoever watched the UK tv show Merlin, the relationship established kinda reminds me of Mordrid and the setup done there.
I highly doubt we will see Winnie again. I bet they are probably dead. Very unlikely a little kid can survive on their own. Cause I think those events happend only a few months after Rick disappeared, so 5 years before present time. Yeah that kid is probably a goner