Maybe Stalin attacks first in this case
The Germans do a whole lot better on defensive, and even send some modest reinforcements to Italy - these are tiny in the scheme of things in the East, but big enough to stop the Allies in their tracks before they have conquered all of Sicily.
Stalin goes ape shit that he is facing the might of the German army, but a couple of divisions of German panzers are enough to stop the Allies.
Mussolini is teetering on the brink of being over-thrown and would push Hitler for an armistice or ceasefire in the East (remember there are hundreds of thousands of Italians in Russia who could return home).
Earlier in 43, Hitler himself has said he'd consider a ceasefire in the East after a major victory. Alt-Kursk is portrayed as one.
So maybe the Russians and Euro-Axis reach an accommodation,
With Germans freeing up forces from the East, Sicily is now untenable in the long-term by UK/US, and an invasion of NW Europe in 43 or 44 is no longer on the cards.
Will the US wait till 45 or 46 until it has a 200 division army to invade Europe, use the a-bomb on Germany in mid-45, or will forces in the US urging the US to end the war in Europe so as to concentrate on "our war" in the Pacific, prevail?