Yes the hair on the tail does grow back, in a few months time (about a year to look back to normal). However pulling fur out is not a good sign, if they are caged together I would keep a very close eye on them, and possibly separate them if they are still chasing each other. Bonded pairs can turn on each other for no noticeable reason. However at around 4-6 months chins go though puberty, and their personalities can change, so that is one reason for turning on each other right there. Think of it like a teenage human, they can be just as moody, and there likes and dislikes can change during that time.
You may only need to separate them for a little while, a few days to a week, just for them to cool off. However it does happen that they end up hating each other, in which case they will need to be housed separately forever. Chins can and do fight to the death, pulling out fur is a warning sign that there is an issue.