Not sure if this was mentioned on this board recently, but already some time ago ICA stopped informing about REP renewal due dates (when they come closer). As the results we just woke up 3 weeks shy from the expiry date. What makes things worse, we would be overseas the time when our REPs expire. While I don't think this would ultimately lead to losing PR status, surely lots of bureaucratic troubles including some fines should be expected.
So mark you calendars or find some other way to remember.
