Before a bad storm they will disconnect the risers and raise them.  But if the platform moves then they may need an ROV (Remotely Operated Vehicle - one of those little mini-sub deals) to go back and a) find b) if necessary repair the BOP and structure so that they can reconnect.  These structures have to be fairly tightly aligned to hit the holes.   There was a post at about the time of Katrina that spelled out all the problems, but unfortunately this morning I can't put my hands on it.  Sensibly I was quoting one of our insiders down in the Gulf, who is now stuck with having to do this (or arranging the same) for their rigs.