Common email pitfalls for social login integrations

We are planning to implement social logins on our site. (Potentially via a service like Janrain or Auth0.) For us the user's email is key, so we will implement only services that expose the user's email.

What are the common pitfalls when integrating social logins for a site? And what are the best practices to handle them?

Examples would be:

• User changes email with his social identity provider, how would we know?
• User deletes his social account? How to handle that?