There is a lot of smoke to be thrown on the official stories that western historians have ladled onto Alexander's Indian adventure. Most of the areas he invaded were not even in modern India but are part of Pakistan now.
The consternation about the Nanda King's unified assets is somewhat accurate – but maybe only on paper – as they were not unified allies – as is described by Chandragupta's successful campaign to unify Northern India and Pakistan of that time by dividing and conquering them. This was a decades long process and not something that Alexander ever probably thought practical.
What can be gleaned from sources is that the campaign was hard fought. Alexander's war aims were not achieved and the march back from India through the desert caused great attrition among his veterans. Nothing as critical as Napoleon's Moscow disaster- nevertheless his rule was majorly altered by his wounds, his losses, the army's fatigue, and his distressing psychological plunges, and drinking.
The return to Babylon created many other crises for Alexander- many of which festered openly and then finally resulted in Civil War after his death.
By the time of his death- most of his gains on the fringes of India had been lost. Only Taxila remained controlled- and they were previously a region under Persian control. Taxila also supplied large numbers of troops and elephants to Alexander that are only rarely attributed to his army- increasing his numbers so he could split his forces and cross the river Hydaspes.
Seleucid and Bactrian influence had to be re-established in Pakistan- only much later did the Indo Greeks temporarily control the northern central regions of India.
It seems, under non hero worship scrutiny, that Alexander did indeed win his battles in India- but at such great cost that they were short lived and his war aims were defeated.
It is difficult to determine how Alexander would have shored up his empire had he lived longer. Seleucus 1st had to march all the way to the frontier to create a border between him and Chandragupta. Creating all sorts of possible battle situations and campaign ideas that we have no details about. Whether there was a "shooting war" is mostly guesswork, but the result created boundaries and deals were made trading land for elephants and non aggression pacts.