I firstly need to preface this by saying that I have never, in over a decade, missed a wedding before, and it would take something very, very serious for me to miss it. Any wedding is a responsibility I take with the importance as if it were my own, so missing it is a very unlikely scenario.
But if this were to happen, I have a very broad network of other photographers who I would contact and ask them to cover for me. Even at short notice, there are many I could ask and confidently depend on.