But I can't see how it's the "eye that does not see" while he still has it?
That's because you didn't read my post carefully.
The prophecy isn't literal.
To Cartagia, G'Kar failed to see his power/majesty/superiority/glory. This confused and annoyed him. What G'Kar did see with that stare, and did not hide, was Cartagia's depravity.
Londo's chance at redemption was when Cartagia asked his advice on what to do about the stare (the eyes that didn't "see"). Londo did nothing. The mistake some make is that they assume any attempt to help G'Kar would have harmed himself and thus ruin his assassination plot. This is not true. He knew how to handle Cartagia and could have made up some BS like suggesting he be blindfolded or knocked out and phrased it in a way to make Cartagia believe he was offering genuine advice, not helping G'Kar.
What world-changing consequences did the removal have, though...except making G'Kar hate the Centauri even more than what he did before?
The prophecy never spoke of world-changing consequences, just of personal redemption. Certainly helping many people is a form of redemption, but so is helping one person, which is a running theme of the entire series (ie, Comes the Inquisitor).
Destroying Centauri Prime would have only delayed the Vorlons by a few minutes – Morden + Londo could be worth those few minutes.
IIRC, killing a planet takes a planetkiller more than a few minutes. At that moment, its presence was urgent at Corianus 6. It would have left had Morden still been there as well.
Still, wiping out a Shadow fleet on your homeworld is a good idea no matter what.
And whether killing Morden (and especially the gruesome display of his head on a pike) is a mark against or for Londo is entirely dependant on your personal morality. For instance, I personally feel it is neither, as I have no remorse over Morden's death but generally find the practice of immediate execution and particularly medieval style body-part displays to be distasteful.
In other words, how did it affect the ebbs and tides of the universe to have G'Kar with or without the eye?
This is a matter of speculation, of course, but I think it's important to G'Kar's personal philosophical development as well as his relationship to Londo. Given the importance these two men play in their worlds' development as prophet and emperor, any subsequent consequences can be quite significant.
If you take the Eye that can't see as being all of G'Kar, rather than just G'Kar's eye, surely you must see that the keeper killed G'Kar when it woke up, and through this surrendering to his greatest fear he saved the man who is already dead.
Are you suggesting that his failure to save the eye that doesn't happen actually happens at the same time as failing to not kill the one who is already dead- that all three chances happen almost simultaneously right before his death?
That's a new one to me.
Yes, it didn't occur to Londo initially that the Vorlons would still consider him to be too much Shadow infulance even after he had blown up their ships etc. However, once the concept *did* come up he was perfectly willing to let Vir kill him to save the planet.
I don't think anyone could of thought of that. Can't blame him for that one. And, IIRC, even he didn't think of it. Vir was the one who realised it.
I personally feel that Londo's true redemption was giving up his freedom to the Keeper at the end of season five.
Londo was always willing to sacrifice for his people, so that act, while noble, does not signify a change or growth.
Ignoring prophecy, I consider his greatest act of growth realising the futility and immorality of the Centauri attitude towards the Narn. Yes, he ordered the end of Narn occupation after Cartagia's death to fulfill his agreement wth G'Kar, but I think he wanted to anyway- a far cry from his attitude in the beginning of the series.