I think it would take some serious international pressure, possibly sanctions to induce the Bush Administration to shut down Gitmo. Even then, I'm not sure they would comply.
As to the question of war crimes, unless an international court decides that the Geneva Conventions apply to "enemy combatants" there will be not war crimes trials, because technically there will have been no war crimes and any individual human rights violations against "enemy combatants" will continue to be tried in US Military courts.
