First, I totally agree that the bow sank first, then the stern. That being said, I would like to draw you attention to the fact that Thayer wasn't the only one with the opinion expressed in his drawing. In fact, Senan Molony just did an article about this very subject in the latest ITHS "White Star Journal".
Not only did Thayer believe the ship sank in this fashion (totally wrong as Mr. Beesley points out in his book) but Clear Cameron, in a letter home to a friend, wrote: "We got about two miles from the Titanic and watched her sink. She just broke up in two and the two ends were sticking up only for about five minutes". In the same article, Mark Baber added an April 23, 1912 edition of the Hudson Observer, in which Thomas Oxenham stated: "When the big ship parted and the hulks drifted apart before going under, we sat shivering and afraid...The halves just seemed to rise out of the water."
Amazing what was seen, or thought to have been seen, that night.
Best regards all around,
Cook