Fem Angron could end up being Red Sonja.
Given their shared memories I doubt she would enjoy the Imperium. Nevermind getting your soul enslaved by Chaos. It's difficult to say where her character would go because from what we actually know of Angron his convictions and views went against what the Imperium was and has become.
I don't think there's a chance to get some of the World Eaters out either. Definitely the hard mode, now that I think about it, because she ultimately has nothing to give this empathy to.
Not gonna lie, Lorgar is becoming a lot more interesting. His initial faith came into being, so should she feel vindicated? But her original also abandoned it with devastating consequences... so guilty? A very conflicted character with limited options all around.
No Legion to fall back on, no supporters, no brothers. Would she want to retreat the path of the past and join the Ecclesiarchy? Something different? Similar to Angron.
Kurze has potential...
Definitely the most freedom and the option that doesn't immediately force us to get into contact with the Imperium. The Night Lords also aren't as tightly bound to Chaos, so it's more a question of gathering them and providing a new purpose. For good or ill.
No idea what to do with Ferrus. Things being shit doesn't change with any of them. The others might have more incentive to change it. But that's my own lack of interest in the Iron Warriors talking.
Edit: I care so little, I even forgot their name. Iron Hands.
Glorious Hawkgirl could go incredibly right or devastatingly wrong. I mean... the worst case I can come up with is that she would be rejected by the Blood Angels + Successors and goes to meet the Lamenters. Interesting in it's own right, but yeah.
All in all it would be a story about living up to unreasonable expectations. It would also lock us in with the Imperium from the start in one way or another. Definitely lots of personal conflict here.