I hate this excuse because it’s so incredibly easy to keep records without keeping the account itself active. I work in healthcare and we have to do shit like this all the time with archiving patients records into an offline storage and then destroying their “hot” accounts to comply with two different incompatible laws.
Opsgenie and PagerDuty let you add them as contacts from within the app and it manages the rotating numbers for you so you can keep using a specific ringtone for them. This is also how they can override DND so you can go back to muting your phone at night and know that pages will still come in.