I do not know if immigration reports to Service Canada that certain people have lost their PR status and their SIN's need to be deactivated. Normally, if you are in Canada and lose your PR status for some reason, you get a departure order, a letter asking you to leave within 30 days. If you don't, this turns into a deportation and they will eventually come looking for you.
If you haven't used your SIN in a few year, for example because you were outside Canada, it becomes dormant and if you later move to Canada again, you would have to request for it to be re-activated.
