jeff masters said on his blog that there are no provisions for what to do in the event we have to retire a greek-lettered storm's name and replace it on the list of hurricane names. one possibility is that the storm will be dubbed greek-letter-2005 and the greek letter will be reused. another possibilty is that the already used greek letter will be skipped over next time the greek alphabet comes into use.

personally, i think they should add in the missing letters, which would give them enough options. languages that don't feature those letters should get with the global thing. alternatively, they could just start with the next set of names; i see no particularly compelling reason against that.