His model is fine. But Orgrimmar will need major rebuilding after the devestation of the Siege.
I doubt they'll just blow up the Underhold since it's nearly complete. Something will be put there. Be it the new Grommash Hold, or a replacement for the Valley of Honor.
I think most of the fortifications will be gone as well, because they were heavilly damaged and it'd be madness to try and rebuild them all.
Aesthetically, I think we'll see a lot more troll huts in Orgrimmar proper, not just the Valley of Spirits.
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Bosses also have special animations that players do not. That's likely a large part of why Garrosh got a new model in 5.4.