I want to say that is allways good and fun to theorise, and I'm not against it.
But, I'm a guy who likes to go by the concrete facts and evidences. And this is why I'm saying that Kuja didn't try to use the Crystal to survive... Because there is nothing pointing to this.
His intentions were clear. He wanted to destroy the universe because he was going to die. Nothing more.

Maybe he tried to use the Crystal to survive. But normaly, in fiction, if something is not showed, not mentioned, or not hinted, during the story... Is because it never happened. Unless there is a confirmation outside of the story(official book, or interview with creators) that confirms it happened.