Only Subscription Administrators (Sub Admins) can promote a user to be a Sub Admin and the one and only Sub Admin for your Rally subscription has left the company, thus leaving the subscription without any Sub Admins.
In the scenario presented above, where there are absolutely no other Sub Admins, Rally Support can promote another enabled user to be the Sub Admin, but only after receiving written permission from a VP-level (or higher) executive.
This written permission is a required security measure to protect your data since CA has no insight into what data is available within a subscription or who should have access to it.
Please follow these steps to have a user promoted to be a Subscription Administrator:
"I authorize CA Agile Central Support to promote <user's name> to Subscription Administrator for the <company name> Agile Central subscription."
Alternatively, the VP-level executive can submit the case themselves to CA Agile Central Support with the above text in the description. This will help speed up the process.