There are two ways in which an ED (End Device) can disassociate from its Coordinator:
The first is a /RESET, if the module receives a hardware reset it will lose the association parameters that are held in volatile memory and it will try to re-associate.
The second method is a DisAssociation request (DA), if the DA parameter is run on the module it will disassociate from its current Coordinator and attempt to re-associate.