When I worked as a Chef, I was there for quite a while.
In that time I had three pretty big bust-ups with separate people, yet we ALL continued to work there.
I wouldn't say any of the are my friends, nor were in fact, but by the time I left we all had an understanding and tolerance.
The point is, that was for a year and we had issues.
I wouldn't know what went on behind the scenes at Buffy, Angel or any other TV show ever made, but will bet any amount of money that along the way there have been arguments, fallings out and maybe even threats to leave, that is the price of working so close together for so long.
We will never know what actually happened on those sets simply because even if someone one day does 'tell all' then it will only be their side of the events.