Nothing at all, as long as the communications properties of the SEPM dont change, then when the purged client comes back into the office, it will connect out to the SEPM using the settings in its SYLINK file, and successfully connect.
As far as the SEPM goes, it will note the HWID of the client, and either link it to existing recrds still in its DB, or create a new client record if the logs for this client have exceeded the log retention settings on the DB).