With changes in strategy, the Poles can do better here or there. Militarily they need to evacuate the corridor, but politically they can't. Perhaps there is political will to do the necessary things. Regardless its hard to win if the Soviets invade just the same. Britain and France left them holding the bag with guarantees they couldn't deliver on.
Cavalry is still useful in 1939 in marshy terrain, deep snow, or where supply is difficult (Eastern front!!!!), so the Soviet were able to use theirs in the Winter 41 counterattack. The Germans won't attack at such a time though where you could have an epic cavalry moment easily.
Perhaps a more likely Poland WW2 win moment, a more likely scenario is where the Polish 1944 uprising gets delayed a couple of days or gets lucky with some fog or something and seizes an airfield, and the Poles actually have a force on the ground when the Soviets roll in, too big to just be rounded up by the Soviets.