Thank you for posting your query on Microsoft Q&A, from above description I could understand that you are lloing for advisory on behavior of your environment when you are using a CMK for encryption of your managed disk and it gets expired.
Please do correct me if this is not the case by responding in the comments section.
When a key is either disabled, deleted, or expired, any VMs with either OS or data disks using that key will automatically shut down. After the automated shut down, VMs won't boot until the key is enabled again, or you assign a new key. Generally, disk I/O (read or write operations) start to fail one hour after a key is either disabled, deleted, or expired
Thanks,
Akshay Kaushik
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