I prefer to use two halyards, both of them for hauling (no static line).  I don't see the advantage of using a static line vs just putting the prussik around the mast, so I use the line the way a halyard is meant to be used.  If both halyards are reasonably tight, it also greatly reduces the shock loading on the remaining one if one fails.  If one of the halyards is internal, I'm not terribly worried about the other being external (like on the mainmast).  But I don't have that option on the mizzenmast, unless I do as Danny did and have a full-length mizzen halyard made up (and drop the sail).  Surely, Henri Amel had a solution to this problem?  Or was he just comfortable going up on a single, external halyard?  I like Paul's idea of a dyneema loop through the shackle... that takes out one failure mode, though still leaves the possibility of the rope failing (or being let go).