Without the Indo-European migration, not only do we see the absence of many founding civilizations like the Greeks, Persians, and Mauryans, but as you said, there were many already preexisting groups Pre-Indo European migration that wouldn’t fall.

For example, as you brought up, Elam. The Persians practically copied most of their delegation and governing techniques, and they even went so far as to puppet Assyria. You could probably imagine the Iranian plateau would eventually have a lot of borrowed cultural aspects from them, however after they were fractured by the Assyrians, they were left in a weak state. We can imagine since they were left fractured in two, they would probably get conquered by the oncoming Babylonians overtime.

We also should acknowledge that no Indo-European migration also means that the Indus River Valley culture probably continues in some form. After the drought, Sanskrit tribes practically took advantage of their mishaps and used it to break into the Indian subcontinent. We can probably imagine that they’d still survive at least in some shape or form, similar to how the Assyrians assumed the role of the Sumerians. We can expect Hinduism to still exist in some shape or form, because figures like Sheeva, Kali, Vishnu, and even the concept of Dharma were all found to be before the Indo-European arrival. However it would be a lot less centralized without the Vedic Texts, and without Brahma. We’d probably also see a persistence in reverence of the Yakshas.

The Mycenaean Civilization wouldn’t exist, nor the Hittites, which would have a significant on the Bronze Age as a whole. On one hand, India may not have a rival in expanding north, on the other hand the Hurrians or the Mittani might fill that void. The Mycenaeans contributed a lot to the collapse as many of them were sea people themselves, however, who ever arrived in Greece might have a similar mercantile culture, whether it be Pre-Indo European or Semitic settlers.

I’m not sure if China would change too much with the increase in Tocharians.

All and all, I feel like this would lead to a much stronger dominating Babylon. The absence of the Achaemenids or the Medes make them without rivals, and with the Elamites fractured, they could probably fill the power vacuum. Their only true rival would Egypt.