In over a decade of photographing weddings, I haven’t missed a single wedding (knock on wood).  I take my job as your wedding photographer very seriously and would never even consider "calling in sick" unless it was dire, and the situation would have to be severe for me to have to miss a wedding!!  That said, if something DID come up, I have a pretty great group of fellow photographers whom I know would step in and help.  And I would do (and have done) the same for them.  Basically, I would do everything in my power to make sure you were covered!