I interpreted the song as an attempt to put all the cliches from past Bond themes into one song and the words are irrelevant, it is the feel of the song they were after, in my opinion.The theme to Goldfinger somehow sprang to mind on my 1st listen for some reason.
Paul Epworth is a producer and remixer and his name on the writing credits implies to me that the song was written for effect and Adele was asked to put lyrics on the top, as long as she included the word Skyfall, so there is no meaning to the words.

Have you heard this acoustic version Skyfall by Jedward???

Alyn