replacing Hitler makes it easier but not impossible for him to delay invasion? maybe they decide to go far enough down the road with USSR and Japan to battle the US first?
There is an actual-logical reason why this would not work and a "hitler-logical" reason why this wouldn't work. The actual-logic was that Germany needed to develop enormous industrial and agricultural power before it took on America. Therefore, the long-term strategy was conquer European Russia and then a generation later have the wherewithal to destroy the US. It does not really work the other way around. At least as important is the "hitler-logic" that he had a world-historical mission to exterminate the Jews of Europe and dispossess the Slavs of Eastern Europe. These were not incidental the Nazism. They were the whole point of Nazism. Therefore, any type of alliance with the Russians (beyond the very brief and transactional) is inimical to the very essence of Nazism. It is roughly analogous to asking why Rommel did not ally with the Jews in Palestine to attack the British in the rear during El Alamein. From a purely military standpoint this would have made sense (and the Jews in Palestine were not exactly fans of the British). The reasons why this did not happen are obvious.
that is really an argument against the OP of this thread, my only speculation was how they could prolong their cooperation. a more Machiavellian leader might have tried to involve the Soviets in an actual shooting war with the Allies or Japan or even just Turkey prior to invading East.
they were also involved in a near war with the US in the Atlantic and the KM leadership was asking for a DoW, they may have thought "ready or not" and they were out of time to capture the resources of USSR.