Problems are rarely solved by running away. Ask him/her to come back and fight his/her corner.
AB is what people make it.
I know of no way of knowing if another user has multiple accounts. It is interesting that others have this insight into both fact and quantity..
The problem, if that is what it is, is restricted to a very small proportion of AB users, the leaving of 1, 2, 10, 50, will not make a jot of difference beyond self-immolation. There is no way AB will be spoiled. This has happened countless times before.