UK and France probably see this as Evil vs Evil, and will not sympathize with either side. Hitler broke their trust in April 1939, and Stalin invaded Finland. Rather, they'll probably hope Stalin and Hitler destroy each other (which likely happens, if the war goes on long enough).
They'll still reinforce Norway as a bulwark (something Churchill planned to do and which Chamberlain will likewise support) which prevents any German invasion in the future.
Stalin only wanted border adjustments with Finland (he knew a full scale invasion would piss off the West). Finland will happily agree and strip the West of any cassus beli for starting war (unlikely the West will be ready to attack before an armistice is called).
Germany is screwed without Soviet aid (they declared war only to discover Poland wanted no part and the West was as ineffectual as they had been at Munich).
With the USSR hostile, the West on alert, and no means to sustain a prolonged war, Germany is screwed...unless the West supports Germany (unlikely after Munich). Hitler either sees economic reason (and makes alliances with the West) which means cutting military spending, or he goes all in and fails miserably.
Of course, this could lead to rapprochement with China to garner what Hitler needs resource-wise. If Hitler were saavy, he'd dump Japan, revive economic ties with China, ally himself with the West as a bulwark against aggressive Bolshevism and thus survive. The West may even return colonies to sweeten the deal thus giving Hitler another public relations coup.