Will exception still be applied to a computer that reported back to SEPM after more than 30 days?
What happens to a computer that reports back to the Endpoint Protection Manager after being purged?
Also, if a computer that is no longer searchable in SEPM (it was purged, meaning no action can be taken on it, for example removing it from the exception group), if the computer reports back, how can you make sure it doesn't go back into the exception group?
It should go into whatever group the client is requesting when it checks back in, either the last group it was in or the originally installed group depending upon what your settings were on the group before it got removed. Once back in, it will apply any new group configuration if anything has changed since it last checked in.
Removing it from it's previously assigned group before purge is a difficult situation, since the computer has the group info but the SEPM no longer has record of the computer. There is no way from the SEPM to stop that client from joining the group it was in the last time it checked into the server. It will need to be done after it reappears.