As said, did Alexander get any additional troops from Macedonia or any other Greek territory to substitute the troops that were lost during his campaign in Persia/India? Or did he have to make do with the troops he started with?
Official historical record lists the Macedonian Army including allied forces as having crossed the Hellespont with 48,100 men. By the time of the Battle of Issus the army was given a strength of approximately 40,000 men. By the Siege of Gaza around 45,000 men and by the Battle of Gaugamela it was listed as 47,000 men. From this it's safe to gather that while Alexander certainly received reinforcements at various points throughout his campaigns it was not substantial. His army maintained its relative strength despite the need for garrisons and combat losses. From that we can conclude he was indeed reinforced at various points by the Macedonians and Greek allies.