Himanshu all that is fine but as far as linguistic decryption is concerned, I find it hard to agree with you due to the following reasons:
1. I find it hard to believe that the IVC was a closeted civilisation given that they had active trade with other civilisations. Why else would you build a large port cities? Moreover, the IV script has been found in far away places giving credence to the fact that they indeed indulged in a fair amount of trade.
this is hard to believe and this is harder to decipher the language but please analyse it on fact based... such a civilization which founded metallurgy, drainage, and thousand other things is still defined as a "land of black mountains" which is coastal area in baluchistan. they were in trade but as I mentioned earlier they were in selling and that excludes other people traveling inland and interacting with harappan.
2. What a lot of people don't realize (I am generalizing) is, the IVC was not limited to the Indus Valley per se. Traces of this ancient civilisation has found extending from Afghanistan to Uttar Pradesh. Therefore it is easy to establish that the IVC was widespread.
I had already mentioned it and this makes it biggest civilization apart from most advanced civilization.
3. Linguistic influence is one of the major traits of an advanced civilisation. Therefore, a civilisation as large as the IVC should have left its linguistic trace in the surrounding regions, even though the primary language did not survive. Take the Sumerian Cuneiform script as an example. Even though the main language died out, the script and alphabets formed the base for Old Persian during the time of Xerxes and Darius.
now we are doing the common mistake of seeing the Indian perspective with western spectacles. if you take example of Sanskrit you can see that here things are different rather then sharing Indian mentality believed in exclusiveness. there is no wonder that none learned the launaguge of Indus valley civilization. the example is not correct on the basis of reason mentioned here.
Certain Graphic similarities have been found between the Indus Valley Script and the Brahmi script but there has been no conclusive evidence so far. Such similarities have also been found with Akkadian writings which follows the Linear Elamite writing system. But like I said, no conclusive evidence so far.
isn't it conclude it well.. no conclusive evidence so far.. may be once that is found we both stand corrected.. till then assumptions on the basis of facts and the basis used for such assumptions is all we have.