So, Sadr levels the mosque with his explosives. So what?
Saddam wrecked the place pulling Shiites out of it in 1991. Obviously, it was rebuilt to everyone's satisfaction, and somehow the Shiites around the world survived the experience.
Of course, if the shrine gets wrecked now, the Iraqi Shiites will (thanks to America) be able to angrily protest it without being dumped by the thousands into mass graves, which I suppose is an improvement for them, although it makes the job of the Iraq government a lot harder.