Perfect language never get decline or dead and never taken over by others languages . If it was/is perfect language for communication then why its dead or not being used for communication today?
I think it was difficult to learn and practice for common people and was language of elite class
some people chant sanskrit words without even knowing the meaning of these words. Its same like some Muslims read/recite arabic without even knowing what they are reading but since these words are part of religious rituals so they memorised it. Urdu borrowed many words from farsi/arabic but that dont mean urdu speaker will understand farsi/arabic speaker or can communicate with them.
It would be great if you make it language of Bollywood. It will be fun to watch three khan or sunny leione/qatrina kaif speaking sanskirit