In addition to the excellent suggestions made by Reinoud, for a long-term legacy viewpoint monitored internally could include.
Delivering ASUP's to an internal mail user for review/collection - Including notification if a critical event were to occur.
Also, outside of DFM/PA, if you happen to use any other SNMP monitor or traps, you could have it check the filer on specific triggers, though if something truly bad did happen, the ASUP alerts would then notify you.
Christopher