The Lord of the Rings' Fellowship was a doomed cause from the very beginning. Gandalf and Elrond assembled a group of nine walkers to parallel the nine Nazgûl, and it was a worthy idea. But there was no way that the Fellowship was going to succeed as a group. There were simply too many trials and enemies on the way to Mordor. Besides, it wasn't like all nine of them were going to waltz up to Mount Doom without Sauron noticing their approach.
The Fellowship had its first casualty in Moria when Gandalf fought the Balrog. It wasn't long after that Boromir fell victim to the Ring's corruption and tried to take it from Frodo. Boromir tragically sacrificed himself to make up for his actions, but the work of evil was already afoot. Saruman's deadly Uruk-hai were upon them, and the Fellowship was permanently broken. While Aragorn, Legolas and Gimli went after Merry and Pippin, Sam and Frodo snuck off toward Mordor. Except their getaway almost looked very different at the end of the Fellowship of the Ring movie.
Fellowship of the Rings' Original Ending Had an Uruk-Hai Drowning Frodo
As the Fellowship was fighting the deadly Uruk-hai army on Amon Hen, Frodo tried to sail off by himself, but Sam wouldn't let him. He was committed to Frodo, so he started following him into the water. But Sam couldn't swim, and Frodo had to circle back to keep him from drowning. That was the way that the movie turned out, but the original version of the story was much different. It still involved Frodo sailing away, but it was much more of an action climax.
In the original version -- as reported by this Reddit thread -- Frodo and Sam were sailing away when an Uruk-hai emerged from the water. It was a full-on Friday the 13th moment, as the Uruk-hai lurked in the glassy water until he suddenly pulled Frodo overboard. They struggled underwater, and Frodo was close to drowning when the Ring slipped off of his neck. The Uruk-hai was so infatuated with the Ring that he went after it and ended up drowning himself in the process. After that, Frodo retrieved the Ring, and Sam pulled Frodo out of the water.
Fellowship of the Rings' Final Ending Was Better Than an Orc Fight
Having Frodo nearly drown at the end of FOTR definitely would have been dramatic. It would have upped the ante and showed just how dangerous it was going to be for Frodo and Sam to venture off on their own. However, that would have been a pretty big departure from Tolkien's version of the scene. In the book, things happened just like they did in FOTR's final movie version. Sam tried swimming to Frodo to show his devotion, and Frodo had to come back and allow him to come along.
Peter Jackson made plenty of minor changes to Tolkien's book (like the exclusion of Tom Bombadil), so changing the ending of FOTR wouldn't have been a problem per se. But it would have been a problem because it would have changed the meaning behind the scene. Action and drama are great, but the ending of FOTR was supposed to showcase that Sam was going to be there for Frodo, even amid the breaking of the Fellowship. So, having Frodo fight with an Uruk-hai would have taken away from the moment that he and Sam had together.