You need to report that to Kawasaki as well as to the dealer. They're going to probably disavow any knowledge on their part of this issue (they always have) but they still need to know that there are problems with the cases falling off.
Kawasaki customer service number (949)-770-0400 then 1, then 5 Tell them that the case fell off on it's own accord and that you are reporting it to the Feds.
Also report this to:
https://www-odi.nhtsa.dot.gov/ivoq/Check the other case to see if there is any 'slop' or up and down movement in the latching system. If there is significant slop then I would take it to the dealer and show them. There are several methods of securing the cases from drilling a hole in the bottom mount and using a lock pin or using heavy round bar stock (I use that), or heavy duty tie wraps. You may want to start new thread here:
http://www.zggtr.org/index.php?board=2.0 .