thomas marshall becomes president
How does that change Versailles?
Assuming Wilson contracts the flu that kills him at the same point he probably contracted it real life
*, then I can't see President Marshall heading to Versailles to replace Wilson at the head of the American delegation. So Secretary of State Lansing would be leading the American delegation there. Lansing was skeptical about the League of Nations, so it's possible that it wouldn't be included in the treaty and even if it were, it would be a weaker organization. In either case, it becomes more likely the eventual treaty is ratified by the United States Senate.
One side effect in either case is that the hypocrisy of the mandate system would be avoided and the former German and Ottoman territory that became mandates would instead be Allied colonies de jure instead of just de facto. It's hard to see how the terms could have been made much harsher against the Central Powers. Indeed, with Wilson gone and thus little hope of his moderating the terms, the Germans might have responded favorably to the officially unofficial approach made by René Massigli about France supporting milder terms in exchange for a Franco-German collaboration against the Anglo-Saxon powers. (Not likely, but not impossible.)
* Wilson was ill during Versailles and while it is generally believed it was due to the Spanish flu, it is not known for sure as like with his later stroke, Wilson kept information on his health private.