You can use the <user> property and its associated <updateEmailWithUI()> method to allow users to update their email address.
Updating an email requires a user to be logged in (which requires they have access to their original email) but to update the email, they just confirm via an email link sent to their new email address.
If a user loses access to their primary email, they would need to rely on that provider's email recovery process to regain access.
If somehow they completely and permanently lost access to the old email address, they will be creating a new account by logging in with a new email address. You may be able to connect the two on your own backend but Magic wouldn't have any way to reliably connect the two accounts.
More information is available in our documentation here.
Note: If a user who signed up with social login attempts to update their email, they will receive an error. Be sure to include error handling in your implementation of the update email flow.