I feel that communication is very important if you have time for it. De-escalation does have some potential to work in some situations. If trying to "reason" with the person fails, or in a situation where it's not just a simple fight (i.e. a self-defense situation where you've been selected as a target and de-escalation is not going to work anyway), it's time for some strong verbal commands, again, presuming you have time.
Verbal commands (e.g. "Back Off," "Stop," etc.) can accomplish a few things. One, there is a chance that the person will realize that he's selected the wrong victim and leave you alone. Two, verbal commands ensure that any witnesses in the area will realize that you are not the aggressor. And finally, verbal commands can "cover your ***" when the BG's attorney tries to rake you over the coals. If you don't give verbal commands, there is a chance that you will be accused of beating this "poor innocent individual" without giving him any direction as to how he can modify his behavior to make the beating stop. By giving commands, you're letting him know that all he has to do to make the pain stop is to leave you alone.
Great post, it's amazing how many situations can be avoided when some one is shown an exit out, and until the exit is presented some will stay even when they don't want too.