I was thinking today about a conference I went to once that had a near-miss with a keynotewho got stuck in traffic without a cellphone. Where was she? Would she make it? If not, who could step in? I happened to be hanging out near the meeting planning staff, so I just watched in awe as they very calmly went about lining up an alternate speaker to fill in while my blood pressure shot up on their behalf. Fortunately, the keynoter glided in just in time and everything went off without a hitch.
Which leads me to wonder: Do you plan to have a back-up, just in case? Is it something you talk about, plan for, have a procedure in place, if not an actual second speaker (which could be a tad expensive, I would think)? Or do you cross your fingers and hope that all your pre-planning pays off and your big presenters make it on time, as they always have in the past? If you work with speakers bureaus, is part of your deal that they provide a back-up should the worst case happen?