The question is how long could Germany fight a protracted war against Britain and France without running out of money or resources without plundering France, Greece,Russia Norway and Denmark to name a few. What would happen to German forces in occupied Norway and Denmark?Would they withdraw , be reinforced or defeated by Britain and France which would allow Iron Ore shipments from Sweden to German to be disrupted.Then you have Russia, without the invasion of Russia, would the Russians annex Romania to gain control of the Oil fields.