Shared Calendar causing difficulty with late spouse's Apple account

My spouse passed away last year and it's time for me to close our mobile phone family plan and set up my own individual plan. This will of course eliminate my husband's phone number.

But my husband's Apple account is still open and if I no longer have his phone number there will be no other reasonable, reliable way to do double authentication when I need to log into his account.( I no longer have his other Apple devices as alternatives to using his iPhone for double authentication.)

The reason I have kept my husband's Apple account open is because we had a shared Calendar for over seven years. My husband was the "owner" of the shared Calendar (ie. he was the one who invited me to share), so if I close his Apple account I will lose our shared calendar from all my devices (trust me I learned this the hard way). I cannot afford to lose the entire calendar of future events and the important record of our last seven years of life together.

So I'm in a bind - I can't close the shared cell phone account before closing my husband's Apple account, and I can't close my husband's Apple account without losing the Calendar.

As most of you here know, Apple:

• won't let Calendar "ownership" be transferred to another family member
• won't merge two Apple IDs into one account (mine), and
• won't let the same phone number (mine) be assigned to more than one Apple ID (so can't use my phone number to double authenticate his account).

Surely I can't be the first person in this situation, has anyone else encountered or heard of how people have addressed this problem?