After you have moderated panel discussions for a while, you realize it is simply a matter of time before some “incident” will occur in the middle of your panel discussion.
Everyone knows that S#!T happens – some of which you have control over (your attitude, the structure and format, your questions), and some simply you do not control (stage or technology malfunctions, external disruptions, or acts of God!)
Meeting Planners International (MPI) has done the work to identify potential issues that could happen in a meeting in their Emergency Action Plan. I don’t think you have to go overboard in your planning, you can put a little thought into how you would respond if such an incident occurred.