Your own custom domain
If you remove or change your custom domain, any links using that domain will continue to function as long as the DNS settings are still pointing to Bitly's IP addresses, and your domain has an SSL certificate.
All domains verified in your account receive an SSL certificate from Bitly. If you remove your domain from your account, even if the DNS settings are still correct, once the Bitly SSL expires the links will not be secure. In this case if you want your links to keep working we recommend you get your own SSL certificate for that domain.
Complimentary domain
If you received your domain through Bitly as part of a free promotion your links will continue to work as long as you're still upgraded. If you downgrade your account to the free version we will not renew your domain with the DNS host when it expires (1 year after receiving the domain) and your links will break. If you're still upgraded we will automatically renew this domain for you and your links will be unchanged.
To have your links work reliably we recommend keeping them verified in your account.