Sellers left the production before all his scenes were shot, which is why his character, Tremble, is so abruptly captured in the film. Whether Sellers was fired or simply walked off is unclear. Given that he often went absent for days at a time and was involved in conflicts with Welles, either explanation is plausible. Regardless, Sellers was unavailable for the filming of an ending and of linking footage to explain the details, leaving the filmmakers to devise a way to make the existing footage work without him. The framing device of a beginning and ending with David Niven was invented to salvage the footage. Val Guest said that he was given the task of creating a narrative thread which would link all segments of the film. He chose to use the original Bond and Vesper as linking characters to tie the story together. In the originally released versions of the film, a cardboard cutout of Sellers in the background was used for the final scenes. In later versions, this cardboard cutout was replaced by footage of Sellers in highland dress, inserted by "trick photography".  Signs of missing footage from the Sellers segments are evident at various points. Evelyn Tremble is not captured on camera; an outtake of Sellers entering a racing car was substituted. In this outtake, he calls for the car, a la Pink Panther, to chase down Vesper and her kidnappers; the next thing that is shown is Tremble being tortured. Out-takes of Sellers were also used for Tremble's dream sequence (pretending to play the piano on Ursula Andress' torso), in the finale - blowing out the candles whilst in highland dress - and at the end of the film when all the various "James Bond doubles" are together. In the kidnap sequence, Tremble's death is also very abruptly inserted; it consists of pre-existing footage of Tremble being rescued by Vesper, followed by a later-filmed shot of her abruptly deciding to shoot him, followed by a freeze-frame over some of the previous footage of her surrounded by bodies (noticeably a zoom-in on the previous shot).  As well as this, an entire sequence involving Tremble going to the front for the underground James Bond training school (which turns out to be under Harrods, of which the training area was the lowest level) was never shot, thus creating an abrupt cut from Vesper announcing that Tremble will be James Bond to Tremble exiting the lift into the training school.  So many sequences from the film were removed, that several well-known actors never appeared in the final cut, including Ian Hendry (as 006, the agent whose body is briefly seen being disposed of by Vesper), Mona Washbourne and Arthur Mullard.

Answer this question "Would unfinished scenes have changed the outcome of the movie?" by extracting the answer from the text above.
So many sequences from the film were removed, that several well-known actors never appeared in the final cut,