I have a channel status for webinars, registered not attending. I treat them generically like no shows, but it's nice to know in advance that they won't be attending so my attendance % doesn't go down.
I typically use a link, which includes a URL parameter. "Click here if you can't attend, but want us to send you the slides & recording" ... then I create a smart campaign, if clicked link = xxx then change status to registered not attending.
make sense? more?