The loss of Ike would be huge, as the man basically held the effort together as the competing personalities struggled against one another. I don't know who would replace him, but they would not be nearly as effect, and the effort could break down to a degree without him. Basically it means the allies are left uncoordinated and could mean the British go for the southern strategy alone if they cannot compromise.
Also, a failure in France means that a southern strategy, probably in the Balkans becomes a major plan, instead of a sideshow. This changes things quite a bit, as the Allies will not necessarily be willing to give up certain places, and could change the alignment of Yugoslavia.
Not to mention what happens to France without being liberated during the war. The longer German control of the country will have massive political effects, but what, who knows? Additionally, what about Stalin's confidence in the Western Allies? I doubt he would seek peace, that is really a bluff meant to force the allies into action, as a surviving Nazi Germany is not in his interests. Rather, I could see him rescind the Tehran treaty, claiming more of Europe as his own as a "penalty" for having to "liberate" Europe by himself. This could mean an earlier confrontation between the Soviets and Allies, with the Balkans as a flashpoint.