Thank you for trying to help. I tried your suggestions, but none of them caused the family calendar to reappear. My husband is the administrator of this calendar, and he made sure the calendar on his devices showed that I had access with editing. I talked to apple support about this, and they really couldn't do anything until I had upgraded all my devices to the latest software version, which I've now done. I've spent most of a day trying to solve this, and need to move on to other tasks for a while.
I'd be happy to read any other suggestions you might have. The calendar disappeared from iPhone, iPad mini, iMac and iCloud but continued on all my husbands devices, including a Microsoft laptop. As a temporary solution, I've recreated the future events on my iCloud calendar, but I'd like to get the original calendar back, if possible.