The following link says that 90% have reduced blood flow, but only 40-50% completely stop.
http://www.webmd.com/hw/menopause/hw228372.asp
Other sites seem to say 90% get little or no blood flow... but there is, at least in my mind, a big diff between saying none and saying reduced.
I am not a fan of litigation, but if you were promised that this would absolutely stop your period then you were given very bad advice. You might want to seek counsel.
Here is a site dedicated to this procedure, with a discussion board for women who have had this or have questions about it.
http://home.att.net/~endometrial_ablation/