Spoilers if you haven't gotten to the Blind Betrayal quest!

I was planning on doing a playthrough where I fight with the Brotherhood alongside my cool Brotherhood companion, Danse. Then, I came back to the Prydwen and had to talk to Maxson, where there were zero dialogue options to save Danse. You can't betray the Brotherhood either, I tried that which resulted in him fighting me. You then have to go on with it, then you have to talk to Danse. You can save him, but he leaves and can't be a follower anymore. There's literally no way to keep him as a follower. I didn't even get his perk yet, I was in no rush because I wasn't expecting to lose the possibility of having a follower out of nowhere.

I've tried everything. I removed him from the Brotherhood faction, killed Maxson, and then gone back to him (he was still hostile). I've reset him, and can't talk to him. I assigned him to the player's teammates list, still won't follow. I've tried just about everything with console commands- except setting blind betrayal to complete, because it doesn't show up in the help list when you search either blind or betrayal.

EDIT: There may be a way around this actually.

Yeah, I'm actually interested in how this deal with Danse is supposed to work, story-wise and without resorting to console commands and such? So, in order to get him as a companion you have to join the BoS, but that questline leads to Danse leaving the BoS (at best), yet by that point you are stuck with them? Is there literally no way to keep him as a companion?

I was able to talk Maxson down, and then Danse said he was just gonna chill at that bunker if I needed him. He's still available as a companion.

Maybe his staying or leaving is dependent on his relationship with you prior to him being made aware that he's a synth?

This, had no issues, only thing i had to do was have the charisma to talk danse down from wanting to die.

So, what will happen if he leaves the BoS but remains a companion and I turn on the BoS? Can I even turn on the BoS at that point? If I can, will he still turn hostile despite technically being their enemy now?

You can turn on the BoS at that point and he won't turn hostile, however you can't have him as a companion anymore. They render him useless for main quest missions after Blind Betrayal. I'm really hoping a mod reverses it. I've changed every faction he's in, and nothing gets rid of the Brotherhood being an enemy while he's a follower. I suppose I didn't try turning on the Brotherhood to see his reaction after removing every Brotherhood faction from him, the quickest way to test it would be to kill Elder Maxson. If you do that and it only opens the trade menu when trying to talk to him, it didn't work. It might be a script causing him to hate you if you're not with the Brotherhood and the same one triggering when he becomes your follower, hence why you can't remove it with faction commands.

To keep Danse as a companion, you have to meet the Speech checks/have a high Charisma and side with the Brotherhood of Steel (regardless of his exile). It's reasonable seeing as how Danse, despite being viewed as an enemy to the Brotherhood, is still loyal to Elder Maxson and his friends in the Brotherhood to the end despite the sour taste he left in their mouth. If you turn on the Brotherhood in any way, he won't bother with you anymore. Either side with Maxson or lose him as a companion until (worst case scenario) a mod comes around to keep him regardless of which faction you end up with in the end.

was able to talk maxson down AND able to keep him as a companion, and actually, the whole scene is easily one of the reasons i think voiced protag worked in this game, as that scene would not have had the impact it did for me had my character been voiceless

I really hope it's possible for someone to make a mod that either A) removes the Brotherhood hates you thing or makes it so he doesn't give you the silent treatment for doing another factions quests. I know it goes against the story/his ideology, but I really want to keep him as a follower.