is now a corpse (kind of) at Red Rocket, is there any way to avoid this and be enemies with BoS? I'm not his biggest fan but wanted to keep companions all together

No, if you side against the BoS, even if he's exiled, he will no longer talking to you. Even while after being exiled, he still believes in the BoS. You can't side with the BoS and keep Danse at the same time.

Well you can side with the BoS and keep Danse at the same time, but he just turns hostile towards any Brotherhood he meets. To have him not go hostile any time you see Brotherhood, you have to finish the Minutemen ending. Although, there is no way to keep all your companions around. Choosing the Institute removes Danse and Deacon. Choosing the Railroad removes Danse and X6. Choosing the Brotherhood removes Deacon and X6. Choosing the Minutemen removes X6.

There is hidden dialog in the files where Danse challenges Maxson for leadership so either the Sole Survivor or Danse becomes Elder which would explain why the Brotherhood are hostile. Maxson probably informed the Brotherhood that Danse is a traitor to shoot on site when the dialog in Blind Betrayal states that Maxson informs the Brotherhood that Danse is dead.