Roosevelt and Churchill would have demanded evacuation of Czechoslovakia and Poland, for instance. As in World War I, the Germans would have been unable to accept an initial peace without completely losing their ability to resume hostilities if, for instance, the Soviets found the Germans to be in violation of its terms.
The conspirators were operating on the deluded hope of desperation.
Of course. The west could not allow status quo ante bellum. I imagine that a retreat to Versailles treaty borders and turning over the Nazi leadership probably would have done the trick.