I can't test this. but i heard. if you knockout alfira. and then do that scene with the new npc showing up. you can continue to talk to alfira
However does that also mean alfira's questline will continue? or are you permanently screwed out of it even if you metagame like that?
Yup, if the player knocks out Alfira she will still talk to them despite the massive attitude loss, but in order to do so it requires naturally extreme metagaming. I believe she still will have her storyline available, despite the negative attitude.