You used to see a dragons head above the stormwind gates, sometimes. And even that was a bit cheesy, since...well, you kept seeing her head there. And now you don't even see, in any mmorpg, this sort of stuff.
Is it really that hard to compromise the idea of a persistant change with ongoing content?
For example, say you had it that a new bad ass dragon shows up. Okay, instead of the first time the dragon is 'killed', have it that it drops into some lava or off a chasm or the ground swollows it up. Or you could even have it that the players take it's head, it goes up on the gates, then after X days, poof, it magically starts to glow and after a few hours, vanishes!
This isn't to just repeat the cycle over and over forever. Just say the dragons spirit is strong enough to return about 100 times or so. This gives alot of groups the chance to take it down a peg. After the hundredth time or whatever, it actually dies for good!
"But then that contents gone"
Okay, here's where you keep the content, but now the dragon has an undead skin placed on it. It's as if it's spirit was too strong to just die and even it's corpse must be batteled. Same loot, same battle (though now with the emphasis of keeping it in it's grave rather than keeping it from marauding the countryside by putting it in it's grave).
What say ye, oh silent traffic that passes my blog in the night!?