Per Bitly’s privacy policy, if an account is inactive for three years, it will be deleted and all your personal information will be removed from Bitly’s systems.
You may also request that your account be deleted at any time in your profile settings.
Once an account is deleted, it cannot be restored.
See these articles for more information about deleted accounts:
How do I delete my Bitly account?
What happens to my personal information, links, and QR Codes after my account is deleted?
What happens to my complimentary domain if I downgrade my Bitly subscription?