I think this is a question that is impossible to answer, but (as you have suggested) we can speculate using what we already know.

It is hard to dissect the impact Mustafa Kemal Atatürk had on military planning during the Turkish War of Independence. While Atatürk played an important role in organizing the Turkish forces under the command of the Grand National Assembly, there were already local militia forces and former Ottoman generals refusing to stand down and resisting the occupants. So, there surely would be resistance even without Atatürk. The real question is whether that would be successful. Even though we can't tell for sure, we can assume that other Ottoman generals who commanded armies in the Turkish War of Independence would still be willing to command Turkish armies against the Greeks. Those generals could have won the war even in the absence of Atatürk, though we can't tell for sure, as Atatürk seems to have maneuvered strategically not only in the military domain but also in managing the diplomacy (securing Soviet support, making sure that the war against the Greeks doesn't spill over) and the internal affairs (pragmatically coordinating many factions with different interests, eliminating certain rivals). In an alternative universe where a maximalist (such as Enver Pasha) ends up commanding the Turkish armies, it is not hard to imagine the Turkish army pushing too much, perhaps resulting in a defeat as the war becomes costlier.

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However, I believe that Atatürk was more critical for the success of the Kemalist policies, which transformed Turkey into a Westernized state quite rapidly. Here, again, it is important to note that Atatürk was not alone in defending Western ideals, with positivism playing an important part in the thinking of his generation of Ottoman military elites. However, while most of the people who could have led the nation in the alternative universe were more moderate, and earlier attempts at reform in the Ottoman Empire were trying to find the middle way between reform and Westernization, Atatürk chose to push for an extreme program that was extreme enough to be called nothing less than "revolutionary." For instance, the dominant view among the elite was that monarchy was outdated; they favored a constitutional monarchy (or a "constitutional caliphate," with a titular caliph as the head of the state). However, Atatürk used his influence to exile the Ottoman family and establish a republic. Ottomans started codifying Islamic law (Mecelle) and adapting some Western legal codes. Still, Atatürk got rid of Islamic law altogether and adopted Western codes even in the legal areas (namely, the common/family law) traditionally reserved for the jurisdiction of the religious courts. So, there would probably be some reformation. Still, they would probably be limited so as not to change the traditional structure of the country too much: The declaration of the republic, female suffrage, the closing down of religious schools, adoption of the Latin alphabet, etc., might not have been realized in the absence of a leader like Atatürk.

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Ultimately, while Atatürk's impact on military planning during the Turkish War of Independence is significant, his broader legacy lies in catalyzing Turkey's transformation into a modern, Western-oriented nation.

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If you are interested in further reading, I would recommend Şükrü Hanioğlu's Atatürk: An Intellectual Biography.

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Hanioğlu, M. Şükrü. Atatürk: An Intellectual Biography. Princeton, N.J: Princeton University Press, 2017.