There's really nothing to it. If you're that concerned, just give it a test run right now. Book a (refundable) ticket on a flight with ample open seats (try AA 1263 LGA-DFW today, for instance), grab a middle seat in a row down the back so you cannot plausibly be harming anyone by occupying the seat for a couple hours, check in, and then cancel it after boarding has begun. It will be a non-event. The only thing I can think of is that maybe the app will say "Go to aa.com to cancel?" but even that is a non-event.