Kuja didn't want to destroy it persay, he didn't want it to go on without him.

While both are similar, they are distincly different things.

If Kuja didn't want the world to go on without him, as he said, if there was a way to continue on his reasoning for wanting to destroy the world wouldn't exist.

And it's no secret he fears death, as thats one of his driving motivations.

So it does in fact hint Kuja would be willing to prolong his own life, but as you said there is no evidence of him trying.

Does this not hint, using in game reasoning and motivations, that there was no way to prolong his life?