please check Grammar & meaning

Forget about the English ! Worry about the idiocy of the idea!

No, it is not correct.

Within decades, a tyranny of the majority will happen in Indian democracy.

Or

Within decades, the tyranny of the majority will happen in Indian democracy.

"Gonna" is a way of writing "going to" which sounds like the way some native speakers would say it. It is not acceptable in formal writing. "Gonna be happen" doesn't sound like English at all. Were i to write this sentence (a very unlikely event), this is how i would write it:

Within decades a tyranny of the majority will occur in Indian democracy.

The worry about majoritarian tyranny in India is not at all idiotic.

I wish you luck in playing with the idea that 'democracy' can be tyrannized by 'the majority' which elects it!
If you are merely saying that 'democracy' is unworkable in India, that might make sense.

You have no idea what the term majoritarian tyranny means. That does not surprise me. The BJP is the largest political party on the planet. I believe i am correct in stating that the membership and affiliated membership of the BJP exceeds the entire population of the European Union. If the BJP achieves a supermajority, it will be able to dictate to the entire population of India, and to trample minorities into the political dust. Apparently, what you know about politics and its workings would not fill a small thimble.

I suggest you look up the definition of 'genuine democracy', with respect to the protection of the rights of minorities.

What a truly bizarre posting style. I suggest that Fresco learn something about the policies and behavior of the BJP before he starts babbling about "genuine democracy" and the rights of minorities.