By giving away the Ionian Islands protectorate the British created a quasi-protectorate over Greece itself. I doubt Britain can or is willing to hold all the islads. She most pobably holds only Corfu and Paxos, as in Gladstone's plan, as acolony. In this TL I suppose Greece comes closer to Russia in the 19th century and thus having better relations with Bulgaria until the Great War. That means that the two Balkan Wars develop quite differently, thus the Balkan map is different, too, with Bulgaria aquiring a great part of Serbian Macedonia and maybe Kavala Seres and Kilkis, and probably Thessalonika becoming a "free city". In that case Greece probably gets Northern Epirus, which complicates things with A-H.
So, what happens in the Great War? Bulgaria is definately not revisionary, so has no reason to side with the Central Powers. On the other hand, Greece is revisionary, but cannot oppose the naval might of Entente. So, if the OE plays as in OTL, I can see both Bulgaria and Greece siding with Entente in 1915, thanks to Russian influence in both. In that case there's no Gallipoli campaign, but, instead, an invasion from Bulgarian soil with the participation of Bulgarian, Greek and Entente forces, which cripples the Ottomans probably in a few months. Is that developement enough to prevent the Russian collapse, the Revolution and the Bolshevik coup? Perharps, but for the thread's sake, let's suppose that things develop as IOTL.
ITTL I can see Greece performing better in the Greek-Turkish war in Asia Minor, since there's no Dichasmos, has better economy and the assistance of Bulgaria. In the end I see Eastern Thrace split between Greece and Bulgaria, the Straights becoming an International Zone-State (LoN control, with guarranty by Greece and Bulgaria), and Greece managing to keep Ionia.
ITTL Greece and Bulgaria are solidly pro-Entente and much stronger in 1939, so there's no Italian invasion, so no operation Maritta...
Not to mention that a British-held Corfu can keep Italy, even with Mussolini out of the war entirely, since the RN can monitor almost all the Italian coastline. If Mussolini nontheless drags his country into the war, he must invade Corfu before he launches an offensive in North Africa. The operation will surely fail, as the RN and the RAF can repel the Italians, like theh held Malta IOTL. What becomes with Mussolini in that case, as soon as 1941?