If Nazi Germany would attack France first and Poland would be not engaged in war, what would be the British reaction to formation of Vichy-like regime.
Would Britain be easier to convice to ceasefire ?
There are a couple of calculations needed for timeline.
1. Has the Nazi-Soviet Pact of 1939 been signed? Otherwise Stalin might seen Germany occupied in the West as a chance to invade all of Poland. This would make the German strategic situation in the East very different then in the OTL
2. Have the German's gone forth with other invasions in the West and North as in the OTL?, Norway, Denmark, naturally Belgium? Our do they cut through the Ardennes directly with their tanks, with a plan like Fall Gelb (Case Yellow)by passing Belgium and the other low countries? A one direction attack plan. Belgium is left alone, not sure if that is goning to happen? But hey.. Without the British and French pushing towards Belgium, the Germans may have less chance of a mass in encirclement of the allies.
3. Again, depends what year this all happens, but if it is early enough, maybe the BEF are never on the continent, that is if Germany pursues a France first policy, leaves Poland for later, maybe the Germans hit the French in 1939? Especially, without the other operations, like Weserubung. But then Britain might be able to seize a more secure position in the North Sea. With better air and naval bases.
It is a possible scenario, but it leaves Germany to weak strageically, if the Soviets grab all of Poland, the British are more secure in Norway. etc.. Not sure the General Staff was confident enough to take a shot at France in 1939, before all the othe confidence building successes of Poland, Norway, Low Countries, etc.. The General staff thought France was going to be a very serious fight, as it was a first rate power(on paper atleast) especially with Britain as an ally. Hitler and the General staff were amazed at how fast France fell. So a direct attack against France in 1939 or so, would be a difficult strategy to envision.