The core of the answer to this question is "We don't know," which I expounded on more in this answer. We just don't have historical sources for how Alexander impacted India after he left. We don't really have historical sources for how anybody outside of India impacted India until after Chandragupta Maurya. Again, for more details refer to the link above.

We can at least speculate on some of the specific details in your question though.

Alexander the Great had already destroyed the power of many smaller rulers and kingdoms of India

To put it generously, that claim is exaggerated. Even in the extremely pro-Alexander histories of later generations, it is clear that Alexander barely penetrated India. The east most point on his campaigns was supposedly somewhere just east of the mouth of the Indus River, in modern Pakistan.

Alexander's early battles in India were right around the modern Afghan-Pakistan border in the region of Gandara, which remained in Greek hands until Seleucus I was defeated by Chandragupta.

Moving a little further southeast, there were more battles and conquests, but the most powerful place in the region was Taxila, which went over to Alexander peacefully and remained the center of power and learning in the region for centuries after the Maurya.

Probably the most famous Alexandrian battle in India was the Battle of the Hydaspes was a costly victory for Alexander that some historians regard as more of stalemate, given that the local king, Porus, was allowed to remain in power. Once again, hardly destroying a kingdom here.

The last major campaign in India was the Mallian campaign, which took Alexander back north, and was really the only all out destructive war that upended two local tribes/kingdoms before ending when Alexander himself was injured. After that, through the whole journey south to the mouth of the Indus, there weren't any more major conflicts.

If Alexander's campaigns and conquests did have any longer term destabilizing impacts on the Indus Valley region, it may have been economic or the administrative in the years after Alexander left. However, there are no sources to answer those questions one way or the other. There's also an open question of how much control Alexander and his successors were actually able to exert beyond the Taxila region. Even in Taxila, there's not really any historical evidence for direct Greek, or even Persian, rule until the Indo-Greek Kingdom. Their influence is even less evident as you get further away from the Hindu Kush.

Alexander certainly didn't destabilize the major power in India at the time, the Nanda Empire. In fact, Diodorus Siculus and Quintus Curitus Rufus both suggest that the power of the Nanda was one motivation for Alexander's forces to halt their advance.

The exact sequence of Chandragupta's conquests is not entirely clear. A dramatic/historical fiction retelling of the events called the Mudrarakshasa says that he conquered the Punjab region first before advancing into Nanda territory. Many other Indian sources don't mention this early Punjab territory, but do suggest that Chandragupta was a relative of the Nanda royal family. The Roman Greek historian Justin implies that Chandragupta's initial army was recruited from mercenaries, presumably from the Punjab region and the fringes of Nanda control. One thing that everything agrees on is that he was educated in Taxila, which might also explain the Punjab connection.

After this small territory in the Punjab though, the basic narrative is the same across all of our sources. First Chandragupta coqnuered/seized control of the Nanda Empire, then he began his campaigns to the northwest and south. Most of the territory invaded by Alexander, and certainly the areas he had the most influence, only fell to Chandragupta after he had an empire at his back.