My question is pretty simple. What exactly happened to the Aryan civilization in India? I haven't read anything to suggest they were wiped out by another civilization or natural causes, so are they the same ethnic group as modern-day Indians?
What Aryan civilization do you mean? If you're talking about the first Indo-Europeans to enter India, their descendants are still there. They make up most of the population of North India and about half of Sri Lanka, while most of the reat of India is Dravidian, the ethnolinguistic group in India before Aryan invasions.