Well Corsica and Tunisia are out of the question none in the Free French goverment wil give them away; a free hand in Yugoslavia and a full recognition of Albania annexation instead are a more plausible gain(plus what was offered in OTL).
Italy entering the war in the last stage will aim towards 'liberate' Austria so to make it again a satellite and block any Soviet attempt to enter that nation.
Yugoslavia can go as OTL if there is a pro-British coup in Belgrade and the man in charge in Berlin decide that is better be safe than sorry, in that case Italy will probably partecipate or be awarded something after the fait.
While no italian partecipation mean that Germany will not be dragged in various adventure like North Africa and Greece, and there will be a point of contact with the world market.
Italy neutrality is a big boone for the Entente or better the British.
Not only they will not need to fight in Africa, saving men and material but they will not need to depleting their reserve in Asia making the job of the Japanese much more difficult...and i not even take in consideration the absence of the mediterrean front and all the british ships now free.
Now the mediterranean is open and the ships don't need to go for the cape route, hell nations can even use the italian merchant marine...overall this mean that the UK is up for a big saving in term of tonnage, time and money.
Remember when i say that now Germany is not distracted by other front, this also mean that Stalin will have less motive to not believe Hitler will remain on his side of the border and not attack.
Not sure why Corsica and Tunisia are out of consideration. UK and US interests would be involved - unless Yugoslavia is also in hand it means Germany can turn Austria and Bavaria into a redoubt, meaning they might both become Communist satellites. If Italy enters the war in mid-1944 then central Europe might find itself less iron curtain and more NATO post-war