Good morning!
How did you mark these leads - were they synced through the Webex-Marketo connector? Uploaded with a status in Marketo? Or just uploaded or added to a campaign in SFDC?
If they are in a Marketo program for the webinar you just use the member of program filter and add the constraint around those statuses, registered and attended... that would be your smart list in this email campaign.
If they are just marked in SFDC in a campaign, I'd create a new program in Marketo and sync with that SFDC campaign and then pull the leads in the way I described above.
Hope this makes sense, it's early
🙂Kim