Gollum's sacrifice

[Lotrelf]

Professor, in one his letters, states that if Sam had not be harsh on Gollum, Gollum would have sacrificed himself.

For me perhaps the most tragic moment in the Tale comes when Sam fails to note the complete change in Gollum¡¯s tone and aspect¡*.His (Gollum¡¯s) repentance is blighted and all Frodo¡¯s pity is (in a sense) wasted. Shelob¡¯s lair becomes inevitable.

And also:

The blighting of Gollum's repentance was due to the logic of the story. If it had happened the entry into Mordor and the struggle to reach Mount Doom would have been different, with the reader's interest shifted to Gollum. I think between repentance and love for Frodo on one hand and the Ring on the other, Gollum would have tried to satisfy both in some queer twisted and pitiable way. He would have stolen or used violence to take the Ring, but having satisfied "possession" he would then for Frodo¡¯s sake have voluntarily cast himself into the fire. The effect of a partial regeneration by love would have given Gollum a clearer vision when he claimed the Ring. He would have perceived Sauron's evil, realized that he did not have the power to use it in Sauron's despite, and realized that the only way to hurt Sauron would have been to destroy the Ring and himself ¨C which would also be the greatest service to Frodo.

Professor says Sam prevented Gollum's redemption, and Shelob's Lair becomes invitable. So, if Sam had acted differently, would Gollum have not taken them to Shelob's cave? Gollum had alread planned to do so, why Sam's actions affect Gollum so deeply that he cannot come back!
Later, he says that Gollum would have sacrificed his life for Frodo's sake. How was that possible when the pressure of the One was too great for the person who was strongest when it came to resisting it? When Frodo "gave in" and could not do what he desired to, how Gollum could have done: knowing he could not use the Ring, and sacrificing himself?