What changes without the Molotov-Ribbentrop Pact

What changes if the Soviet Union does not sign the Molotov-Ribbentrop Pact?

Poland probably still falls, but the Soviet Union may be better prepared when Germany invades.

The Soviet Union was unlikely to let British and French forces cross its territory to support Poland. Poland also had strong reasons to distrust Soviet troops after the conflicts of the 1920s and 1930s. The largest change may come later: Stalin has less reason to dismiss warnings that Hitler will attack. Better Soviet preparation could reduce Germany's initial success in Operation Barbarossa even if Poland's immediate fate changes little.