With how terrible and dangerous the journey to Mordor was, The Lord of the Rings ends on a relatively positive note. But still, with Frodo and Sam separating from the Fellowship, there was a very real chance that things could've gone south, and Sam would've been left to carry the One Ring. Especially after Frodo was stabbed by Shelob, Sam fully believed he had to finish the journey alone. And so, if Frodo had died there and then, could Sam have destroyed the Ring by himself?
Before tackling the corruption of the One Ring, there's the physical aspect of making it to Mount Doom. If Sam was all alone, he would've been great at sneaking across Mordor, as the Orcs couldn't even detect two Hobbits making their way through the land. Once at the volcano, Sam was able to carry Frodo on his back, so making it up alone would've been no problem. The big issue would've come from Gollum, as Sam would be left all alone to fight him -- and most likely lose.
Even if Gollum wasn't a problem, and Sam finally made it to the fiery chasm, there's the debate of whether he would throw the Ring. Seen with both Isildur and Frodo, neither of them could bring themselves to destroy it, as the Ring always corrupted them in the final moments. However, Isildur was greedy and always wanted power. As for Frodo, he had been carrying the Ring for almost an entire year, so he was far more corrupted by the time he got to Mordor.
With Sam carrying the Ring for far less time, paired with his incredible kind-heartedness, it seems possible that he would destroy the Ring. Yet, it's easy to forget just how powerful the Ring really was. In The Lord of the Rings novels, Tolkien made a point of showing the Ring's growing corruption with every step closer to Mount Doom. And even with Sam's short time holding it, the weight began to take hold of his mind.
After just a few minutes of carrying the One Ring, Tolkien writes, "No sooner had he come in sight of Mount Doom, burning far away, he was aware of a change in his burden. As it drew near the great furnaces where, in the deeps of time, it had been shaped and forged, the ring's power grew, and it became more fell, untamable except by some mighty will." And so, with Sam not even at the mountain, he already felt as if the corruption was too much to handle, and that "Already the ring tempted him, gnawing at his will and reason."
Other than Frodo, Sam was probably the best member of the Fellowship to bear the Ring. Yet, it was still too much to handle. Judging by the Ring's quick impact on him, it's unlikely Sam would've been able to destroy it. It really goes to show just how terrible a burden the One Ring was. While some fans have criticized Frodo for not putting in enough effort during thee journey, the battle within his mind was far worse than anyone could imagine.