Say Germans don't want to agree to territorial loses. In June 1919 they invade Poland to regain Posen. As result Western Allies invade Germany from the west. War restarts. What happen then?
Germans are unable to continue war for long time, they were exhausted and would soon face shortages of almost everything, including food. So they're beaten again, within weeks to 2-3 months . But this time their position is worse:
-Russia is out but now Poland is active side of this war (Polish Blue Army that fought on the Western Front was transported to Poland then and relocated to Posen and Corridor to protect Poland's new western border in the case of German attack), not newly emerging state taking opportunity of WAllied victory over Germany, so being among winners Poles would be given more lands (whole Upper Silesia, Danzig).
-Britain would not be lenient towards Germany anymore, especially because desperate Germany would seek for alliance with Bolsheviks and vision of German-Bolshevik alliance would be terryfying for everyone.
- For the same reason there is more pressure to aid anti-Bolshevik forces. Whites are still doomed (especially with Allies attention distracted by restarted war with Germany) but Poland would recive more support once war with Germany is over (and with Danzig in Polish hands it is easier to transport western supplies to the Polish Army)
-Czechs would not invade Poland to get Teschen now when Poland is fully supported by WAllies and part of new Entente. So there is plebiscite in Teschen and better Polish-Czechoslovak relations.
-Germans tried to reverse Versailles by force and were beaten almost immediately. Would they try again? They should be more cautious as result.