Does my license auto renew? Or do I need to take action?
Can I keep on using the plugin after it expires, but I then cannot update it? How does it work?
There is no any auto renew or auto billing. You will need make new purchase manually if you need to prolong a subscription/membership.
You can keep using plugin after membership expiration. It will work until stay compatible with future PHP/WordPress updates. You will lose only updates and support if decide to not prolong a subscription.