Good evening Jane and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the calendar disappearing on you. Yikes!
I would love to help you with this topic.
As a first step, I would recommend to try temporarily reverting back to a default WordPress theme such as twenty-sixteen to see if the calendar appears.
If so, you might want to revert back to your theme, but this time try different settings for Events Template under Events -> Settings -> Display.
For now, I would not overly worry about the license key issue.
In the meantime however, I would recommend updating the Events Calendar Pro to the latest version manually on the staging site.
Let me know how that goes.
Best regards,
Geoff B.