Poland was a Warsaw Pact (Soviet alliance) member; other NATO nations, the UK, West Germany, Spain and Italy, would certainly have been behind us.
Don't bet the mortgage on it. NATO was configured as a defensive alliance. Any attack on A MEMBER STATE was as an attack on all. But Poland was NOT a member state. Can you imagine France or the Benelux countries joining the US in a war to drive Russians out of Poland?! And West Germany would have had a hard time joining in; her armies would have to march through EAST Germany to reach the Polish border. I don't the ca. 400,000 soviet troops in East Germany and 150,000 or so East German NVA troops would have simply moved out of the way.
Polish armed forces would have fought against the Soviets, and commanders that ordered troops to fire on fellow Poles would have been killed by their own troops.