It is not a matter of debate as there are speakers even today. Declining definitely, but still significant.
http://en.wikipedia.org/wiki/Sanskrit#Contemporary_usage
The 1991 and 2001, census of India recorded 49,736 and 14,135 persons, respectively, with Sanskrit as their native language.[1]
http://www.mangalorean.com/news.php?newstype=broadcast&b...
But surprisingly, today in Mangalore, there is one unique family where all the members are using Sanskrit as their mother tongue and they all interact with each other in this language only. Seems highly improbable but nevertheless, it is true.
I think one reason for the decline is that you need to be pretty intelligent to learn Sanskrit (vs say Tamil or English). I sort of feel that the human race itself was more smart a few thousand years ago. (See http://rt.com/usa/news/intelligence-stanford-years-fragile-5...)
The way we describe grammars can be attributed to one of the first Sanskrit grammarians, Pāṇini.
http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form
The idea of semantic roles can also be traced back to him.
Otherwise, it is like trying to go to a planet in the Andromeda galaxy without first ever going to the moon. Never gonna happen.
http://www.aaai.org/ojs/index.php/aimagazine/article/view/46...
There are still native speakers of Sanskrit. The cool thing about Sanskrit is that not only is its syntax formalized, but people have tried to give an account of its semantics over thousands of years.