It really depends on your Mailchimp lists but you can do advanced setup like:
Syncing Mailchimp and Livestorm is our number one use case. Thanks to Zapier you can really go deep inside Mailchimp and do amazing things in terms of retargeting. Let's dive in.
The easiest way to sync both platforms. Pick the trigger "New registrant" on "All Webinars" and add a Mailchimp action to create or update a subscriber. Turn your Zap on and that's it.
Go back to your Livestorm trigger and pick "Send Registrants When Webinar Ends". Then add a filter action that check if the key "is_attendance" is set at false. This means that the attendee did not join the webinar. So the condition should be: if "is_attendance" = true then send that person inside Mailchimp.