Deleted billing leader on Pro account

[ackernaut]

If a user invites others, upgrades to Pro, then deletes their account, the org gets left without a billing leader:

• Create an account (user A)
• Invite 2 others
• Upgrade to Pro
• Delete user A
• Other users are still in the org (good) but there’s no billing leader (sad panda)

Originally posted by @ackernaut in #3910 (comment)

[ackernaut]

Starting this as a discussion on how to handle cases:

• Pro org with 1 user, now deleted
• Pro org with many users, but left without a billing leader

[github-actions]

Stale issue

[jordanh]

Still a thing, iceboxing for now