Our space was previously using email based accounts. However, we’re switching to an oauth based approach. Because users are so heavily tailored to emails, we cannot migrate existing user accounts from email to oauth, only delete old accounts and ask individuals to make new ones. This will completely decimate our workspace’s audit logs and other user & time based data (such as created time and created by fields).
It should be noted that the reverse works just fine. An oauth based account can be migrated to email without issue.