Mark Mawson Welcome to Microsoft Q & A Community Forum.
- If you delete a virtual machine that was protected by an Immutable Recovery Services Vault, the backup data for that virtual machine will be retained in the vault and will not be deleted. However, since the virtual machine is no longer present, the backup job will fail and you will receive an alert. As you mentioned, since the Immutable vault is locked, you cannot make it mutable again and make changes. Therefore, you will need to create a new Recovery Services Vault and configure backup for the new virtual machine in the new vault.
- A locked immutable vault is a vault that has immutability enabled and cannot be disabled. This means that no operations that could result in loss of backups are allowed on the vault or its protected items. However, this does not mean that the vault is independent of the Azure subscription that it belongs to. If the Azure subscription is terminated, the vault and its backup data will also be deleted after 30-90 days before permanently deleting the data, regardless of the retention period of the backups.