This theory has been broken to pieces by many western scholars long time back. David Frawley is one of the key personality who proved that aryan invasion theory is a myth.
Human migration is a better term than "invation" wrt the time we are talking. The Indus script travelled south and continued to be used in much later times may be as ornamental or with a lost/morphed meaning. Please recollect the earlier threads on the Sembiyan Kandiyur celt ( 1200 to 800BCE ) and the Anaikottai bilingual seal of Sri Lanka ( not earlier than 300BCE) .
This finding re-establishes that the Indus seals could be read using dravidian etymology.
There were no aryans or dravidians... only Indians.