Steven Biel in his book "Down with the old Canoe" mentions a 74 year old Mr Henry Adams that booked to sail back on the Titanic. I would agree that Ismay, Fry, Harrison, Andrews, Chisholm, Parr and others from H&W were very likely to return on Titanic, as they had no business in NY and were only taking the Titanic to observe her in action.
Before Olympic reached New York on her maiden voyage, newspapers were already printing the numbers booked to sail back. I don't recall the same thing for the Titanic. Not even after her sinking. I do recall reading in a newspaper mentions of White Star quickly rearranging travelling plans for those booked to return on Titanic. No numbers were mentioned though. Unfortunately there is little hope that any lists survive of Titanic's return bookings.
I do recall reading somewhere (for the life in me I cannot remember where) that a steward commented on the modest number of people taking the Titanic to New York, and then commenting that they received a marconigram mentioning that they a more heavily booked on the return trip. I don't know if it said booked full, or just much better booked than the first leg of the trip.
As for Capt. Smith, Mark Baber has done a great job transcribing some of Olympic's maiden voyage articles. These were from June 1911 and one of them talks about how Capt. Smith was to retire by the end of 1911 and who was to command the other ships Titanic and Gigantic (aka Britannic - this ship was still called the Gigantic as late as August 1912). I think the articles are still on ET. Have a look under Olympic's maiden voyage thread. I may be wrong as to where I read it, but I definitely recall it was from one of the articles Mark transcribed. Perhaps he would be able to help out on this.
Regards,
Daniel.