I just had another thought on the subject.
It was greed that lead to the creation of the ring. Sauron desired control over others so much he created powerful rings for others. Then he created his one ring to rule the rulers. Greed forced him to put much of his own power into the ring so that he could control the others.
And it was that very same greed in the ring that lead to it's destruction. The book with it's Eucatastrophe aside, the movie is better (in this thought process).
Think of it, without a eucatastrophe to drop Gollum in the pit, the ring would have survived. Instead, greed for the ring, on both Frodo and Gollum's parts, lead to the rings destruction.
I know what I'm thinking but having trouble with the words, so bear with me.
Frodo, as the hero, set the stage for the rings destruction. Any single person, regardless of strength, never could have tossed the ring in the fire. At the last they would have been overwhelmed and claimed the ring for their own. If they had not already done so on the road there.
So it is only by both Frodo and Gollum being present, that the greed inspired by the ring turned to it's own undoing. Only through the struggle of Frodo and Gollum could the ring have made it over the edge.
Jackson quite nicely, and with a minimal change, made the rings destruction from something that just sort of happened (or was caused by a higher fate), into the destructive nature of evil destroying itself.
Then, once you get your head wrapped around that, think on this comment from Gandalf. He said that it never entered Sauron's thoughts that they might try to destroy the ring. But what if Gandalf was wrong. Perhaps Sauron did think they might try, but still never worried about it. He had that base covered already. The power of the ring simply would not allow someone to do it. The power of the ring would have corrupted the person and forced them to reveal themselves to him.
That, and any party big enough to overwhelm the ring bearer and force his hand, would have been easily picked up by his own forces.
So we have Sauron defeated by the truly most unpredictable of things. A power struggle over the ring, that made an oops and dropped the ring in by accident.
I guess there was still some level of Eucatastrophe, but it wasn't as big as the book originally put it.
