Well, there's actually a reason that Aerith died. And that would be because she was the last remaining Ancient and therefore the only one of the party members who could exert control over the Lifestream in death. You remember at the end of the game when Holy was actually helping Meteor more than it was hindering it and everything seemed lost. And then the Lifestream came bubbling out of the ground and was headed towards Meteor and Aerith's face is visible for a brief moment just before the credits start to roll.
Well, we know that whatever the Lifestream did, it saved the Planet. We also know that the Lifestream was caused by Aerith. This same effect is visible in AC when the Lifestream comes gushing out of the ground in the church towards the end. So, Aerith needed to die, else the world would have been destroyed by Meteor. That is why the story worked out the way it did. Aerith's death had nothing to do with who Cloud did or didn't love.
