It's been 4 years but this bug still hasn't been fixed. It kinda ruins the ending for me. There's a few observations I've made about this bug that might help someone fix it; It's not exclusive to Zinyak's head. A similar glitch happens with gun magazines sometimes, they'll become attached to the player's hand and won't disappear until you reload. It happens because you're knocked down a split-second before the final cutscenes start. After the quicktime event where you pull Zinyak's head off, something happens to knock the Boss over. No idea if it's a CID or what. It happens every single time I have played the game over the past 4 years, and did not occur before that. The bug doesn't occur if you load the final cutscene through Sandbox +, hence why I believe the previous point is the cause I am not experienced with modding so I don't know if a fix would be easy, but there's two solutions I'd accept; Just make the Zinyak head invisible. So the bug would still occur, but it wouldn't affect the game visually. I don't know whether this would make Zinyak's head on his body invisible in the On Track dance scene though. Edit the mission script to either move the boss after Zinyak is defeated, slightly move the location of the final quicktime event, wipe all enemies, or something. Once again I'm not a modder so I don't know if this is possible. I hope something can be done about this. We all know how buggy the game got after the 2016 patch, and while this wouldn't fix the constant freezes, it would at least make the ending a bit nicer to watch.