When FDR was looking for someone to replace Henry A. Wallace on the VP slot in 1944, one of the people he reached out to was Wendell Willkie, the 1940 Republican nominee and one of the most liberal members of the party. One of the promises he made to Willkie was that, after the war, they would create a new liberal party created from the left wings of the Republican and Democrats. Willkie, who had just failed to gain the 1944 Republican nomination, was somewhat interested, but he cut off the talks when details were leaked by the press.
First off: was a Roosevelt/Willkie ticket a real possibility? Roosevelt had a habit of making false promises to potential running mates, and it would be hard to get a Republican nominated by the Democratic Convention, especially since the anti-Wallace faction had mostly gathered around Truman.
Second, what consequences would this have? IOTL, Willkie died in October of 1944, but this was only after he refused medial treatment despite suffering from multiple heart attacks, so his death could be butterflied away by making him go to a doctor sooner. Assuming that FDR dies around the same time, how would Willkie handle the war and domestic situations? Considering that he would likely face hostility in both the Republican and Democratic parties, would he try to set up a new liberal party?