If they still had Gandalf...

[aelithes]

I agree with Ruoutorin that fate has a part to play in what transpires in LOTR, but it's certainly not absolute, nor does Tolkien wish us to think so; he is careful to not make his characters mere puppets to fate.

The most conspicuous and efficacious piece of evidence for this is that Frodo was in fact foreseen to fail (and fail he did) - it was precisely the compounding of various expressions of 'free will', the anti-fate (e.g., the pity of Bilbo, the pity of Frodo, etc.), that resulted in the ring's inadvertent destruction.

But to get back to the topic! Yes, the matter of still having Gandalf is definitely too big to wrap my head around. The repercussions would've been huge. I can only say that in terms of the Fellowship, it probably would have stayed together rather longer than it actually did. But as Galadriel says, the seduction of the ring would have consumed them all, and I am much more uneasy about Frodo's chance of success if he's surrounded by those who feign friendship while harbouring secret (not-so-secret) desires (Boromir, Aragorn, the rest of the Fellowship, inevitably) as opposed to those whom he is openly suspicious of (e.g., Gollum). It's an inexplicable hunch, but I just think the ring would not have made it closer to its goal than Minas Morgul, if that.