I think such endings would underestimate the effect the ring did have on Gollum. We saw Bilbo's rapid aging afterwards and Gollum was (through duration of posession as well as evil means by which it was obtained and frequent use) a lot more under the influence of the ring. I think that a sudden change of mind at the spot where the power of the ring was probably greater than anywhere else would have been rather implausible.
Also Gollum himself (when confronted by Sam just before entering Samath Naur, the door into Mount Doom) is very concrete about what the destruction of the ring will do to him:
"Lost, lost! We're lost. And when precious goes we'll die, yes, die into the dust." He clawed up the ashes of the path with his long fleshless fingers. "Dusst!" he hissed.
I know, but Gandalf himself said that Gollum might be capable of some good, and, indeed, he he was, as he led them the only way in that would have worked (Frodo would have tried going through the Black Gate had Gollum not come.)
Also, the fact that Gollum is kind of a Hobbit too may make him stronger than men and stuff. Anyway, Bilbo came very close to killing Gollum when he took ownership of the Ring.
As for Deagol, I don't condone what Gollum did, but, well, in a sad way, he might have done his old friend a favor by killing him rather than letting him be the one driven mad and bad by continuing to have it.
Also, as I said, the Nazg?l would be very near and Gollum would realize that he's not gonna be able to keep the Ring anyway and so would do the right thing for once when Frodo failed.
Yes, he'd die right afterward, as he says so, and hence couldn't be rescued by the Eagles.
Anyway, Gandalf says that Gollum actually really hates the Ring and this is his chance to finally be rid of it and die in peace. Gollum wouldn't destroy the Ring, but I think Smeagol would.
Anyway, Gollum would know the evil effects of the Ring better than pretty much anyone and so would want it gone the most.