Yes, this is very true. It it correct to say that the entire civilizations in the Indian city was lost to history. We have witnessed Tsunami destroy very precious things in the country's that it has occurred. Tsunami is a very terrible calamity and it has also caused lose of lives.
There are rumors about the lost city of Atlantis for one, which may or may not be the lost city that was found after the Tsunami. The world has changed and it is quite possible that there are other ancient civilizations lost to time that we have left to discover.
Human civilization has been around for thousands of years, if not millions of years. We have no idea the multitude of societies that may have existed that we know nothing about. The part of human history that we know is a relatively short window. Brief glimpses like these make it clear how much unknown is still out there.
The stone remains found by archaeologists in India may be a good indication that there are more lost civilizations to discover. Time and geologic changes have hidden some of them from view and since many existed before written history, there are no records other than anecdotal ones of them to try to find.