No one asked the important question... was it go-home leg?

In all seriousness, there is no excuse to not have a reported open panel checked out. You may waste 15 minutes, but a few calls to ops ought to get everyone in position to correct your issue quickly. You won't even stop the pay clock.

Even if the panel does close somewhat due to slipstream, it is an unsafe condition. The door will not latch, but ti will vibrate at high frequency. That is loud and annoying to the passengers, and excessively stressful on the door and hinges. You never know when that door will give, and you don't want to be responsible for contributing to another Concorde-like accident.