Woo-hoo! I whooped Crisis Core! (spoilers)

Finally! I pimpslapped Minerva (the “secret” boss) and received the Divine Slayer and Heike Soul as my rewardz. Along the way, I also picked up all four pieces of Genji stuff. My Zack is now a frigging god! Of course, he still gets beat down by the Shinra grunts during the pre-ordained “final battle,” there’s apparently no changing that. I “lost” with tens of thousands of HP still to my credit.
Now, apparently, if I wish to do so I can roll through the game again, perhaps on hard mode, and drive my enemies before me.
If I do so, it’ll be less fun than the first time through. Can the end be changed or does Zack die no matter what?