A business rule on sys_user that says:

before Insert

condition current.active.changesTo('false')

var group = new GlideRecord('sys_user_group');

group.addQuery('manager', current.sys_id);

group.query();

while(group.next()){

group.manager = current.manager;

group.update();

gs.eventQueue('group.manager.changed', group, group.manager, current.name);

}

var grmember = new GlideRecord('sys_user_grmember');

grmember.addQuery('user', current.sys_id);

grmember.query();

while(grmember.next()){

grmember.deleteRecord();

}