The Witch-King of Angmar stabbing Frodo Baggins was a shocking moment in The Lord of the Rings, and had Frodo died Middle-earth would have been a very different place. Peter Jackson's The Fellowship of the Ring saw Frodo take a seemingly fatal blow from the Ringwraith leader's Morgul-blade. Things worked out after Frodo was stabbed by the Witch-King in Fellowship, as the quick actions of Aragorn and Arwen preserved the young Hobbit's life. Had he not been saved, this dark weapon would not only have killed Frodo but condemned him to a fate worse than death.
However, an alternate timeline where they were not fast enough would give Lord of the Rings a completely different story and a far bleaker ending. Frodo was perfect for destroying the One Ring, while Samwise Gamgee and Gollum were also integral to the mission's success by helping it get to Mordor. Had any of the trio died earlier, the Ring would almost certainly have never been destroyed, and Sauron would once again have dominated the world of Men, Elves, Dwarves, and Hobbits.
The Witch-King’s Assault On Frodo Nearly Turned Him Into A Wraith
As mentioned in The Fellowship of the Ring, Frodo would have become like the Nazgûl, a Wraith, had he not been saved. However, what was not mentioned in the movies was the specifics of what Frodo's fate as a Wraith would look like. In The Fellowship of the Ring book, Gandalf confirmed that Frodo would not become one of Lord of the Rings' Ringwraiths, as he would no longer possess the One Ring, but would rather become a "lesser Wraith," wandering Middle-earth in eternal torture.
Of course, this would have meant a swift end to Frodo's adventure as the Ringbearer. The Council of Elrond would likely have convened with a more solemn atmosphere as the Hobbits, Aragorn, and Gandalf mourned their fallen friend. It would also have meant that Frodo would have never met the other members of the Fellowship, and would never have reunited with Bilbo in the movies, who would all have been devastated by his fate.
Samwise Gamgee Was The Obvious Successor To Frodo
It is likely that the remaining three Hobbits, Merry Brandybuck, Pippin Took, and Samwise Gamgee, would have still followed the party to regroup in Rivendell. However, whether they would have still sneaked in to watch the Council of Elrond convene and discuss the fate of the One Ring is unclear. It is more likely that the three would have sought to return to the Shire, feeling defeated after losing their friend. However, a new Ringbearer would still have been required to ensure the Ring reached Mount Doom. The purest person present at the Council, Samwise, would have been obvious to a being as wise as Gandalf the Grey.
Even before his triumphant attack on Cirith Ungol in Return of the King, it was clear that Samwise was the bravest and most loyal Hobbit among the Fellowship. He had even stood up to the Nazgûl to save "Mr. Frodo," before being pushed aside. It would have been likely that Gandalf recognized these qualities in Sam. He would also have been very aware that easily corrupted men like Boromir would seek to use the Ring for themselves. Knowing the One Ring wouldn't corrupt a Hobbit as much, and seeing Sam's natural bravery, Gandalf would have likely brought Sam to the meeting and made him the new Ringbearer.
Sam’s Journey With Gollum Would Not Have Lasted Long In LOTR
After Samwise took the Ring, the movies would have possibly played out similarly to how they did with Frodo. Gandalf would have likely seemed to have been killed by the Balrog of Morgoth, Boromir would have attempted to steal the Ring and then be killed by the Uruk-Hai, and Sam would have decided to go off alone. However, this time he truly would have been alone. He would have ventured on the path towards Mount Doom without any other members of the Fellowship, leading into the events of The Two Towers. This would have marked the greatest departure in the story, as Sam's relationship with Gollum would have doomed Middle-earth.
As in The Two Towers, Sam would have met Gollum on the path to Mordor's Mount Doom. However, unlike Frodo, Sam was immediately hostile toward Gollum in the actual movie. In the darker timeline, Sam would have been feeling the weight of the Ring and may have shared more of Frodo's compassion for a fellow Ringbearer. Sam and Gollum may have traveled together for a while, but their conflicting personalities would have inevitably clashed and probably turned violent without Frodo to mediate. It seems likely that Sam and Gollum would have quickly ended up fighting, with one of them potentially killing the other for the Ring.
Despite Sam’s Good Heart, Middle-earth Would Be Doomed Without Frodo
Without Gollum to guide him, Sam would have ended up lost in Mordor, just as he and Frodo were before meeting Smeagol in The Two Towers movie. Sam would have likely ended up being killed by orcs or other servants of Sauron. Although Sam would have probably avoided the temptation of the Ring as much as possible, his isolation and brutal encounter with Gollum (assuming he survived) would have left him desperate and alone. Whether Sam was caught or killed, the Ring would have inevitably ended up exactly where it wanted to be, on Sauron's finger.
With Sauron back in control of the One Ring, the forces of Middle-earth would have been powerless to stop the dark lord. The Free People were already hopelessly outnumbered by his forces when destroying the Ring was the only way to defeat Sauron in Lord of the Rings. As the Ring would have amplified his powers, it would have been completely impossible for anyone to stop him, even an incredibly powerful being like Galadriel. Essentially, the seemingly small act of the Witch-King successfully killing Frodo in the first Lord of the Rings movie would have created the darkest timeline for Middle-earth.