If Italy stays in the war after 1943 as an Axis member (with or without Mussolini himself), the overall impact on the war is minimal. OTL, the defection was basically a wash for the alliances, since sizeable numbers of Italians continued on as German puppets in the Social Republic. The Italian peninsula is perfect for a fighting retreat by Axis forces without complete Italian participation anyway. In fact, if the Italians fought alongside the Germans in this stiff defense, the general opinion of Italy as co-equal with Germany and Japan in the Axis might be strengthened.
Germany itself will be overrun by the Wallies and Soviets at about the same time and that will end the war, even if the Italian front is a going concern. Then peace happens. Unless, the Soviets actually penetrated in to Northern Italy, I doubt they could make any case for dividing Italy into occupation zones including a soviet zone, but it is not out of the question that Italy could still be divided into US, French, and British zones, or that it could lose territory to France. However, it was apparent even in 1945 that Fascist Italy was not in the same league on the World War 2 Evil-o-Meter as Nazi Germany or Imperial Japan, so the Italians might get a fairly soft peace. I suspect Italy would quickly be reintegrated into western Europe.
Germany itself will be overrun by the Wallies and Soviets at about the same time and that will end the war, even if the Italian front is a going concern. Then peace happens. Unless, the Soviets actually penetrated in to Northern Italy, I doubt they could make any case for dividing Italy into occupation zones including a soviet zone, but it is not out of the question that Italy could still be divided into US, French, and British zones, or that it could lose territory to France. However, it was apparent even in 1945 that Fascist Italy was not in the same league on the World War 2 Evil-o-Meter as Nazi Germany or Imperial Japan, so the Italians might get a fairly soft peace. I suspect Italy would quickly be reintegrated into western Europe.