HI Rahul,
Generalizing removes machine specific information so the image can be used to create multiple VMs. Once the VM has been generalized or deprovisioned, you need to let the platform know so that the boot sequence can be set correctly. So to add this is a irreversible process. Once you generalize the Virtual machine, the VM becomes inaccessible and the operation cannot be reversed back.
Please contact Microsoft asap to assist in this process either way you can restore from snapshot or have any backups?
https://azure.microsoft.com/en-ca/support/create-ticket/
Hope this helps.
JS
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