Geography?Search for some other excuse.If geography was the reason India would have disintegrated a long time back.Major disagreement here.
Geography keeps India together, nothing else. You should take time to go through some of the arguments against Pakistan raised by Muslim Scholars.
Your insistence on a civilizational narrative is actually divisive. Your fears are more likely self-fulfilling prophecies.
The fact that Pakistan exists allows you to make such statements. Had there been no Pakistan, you would not have been able to say all this.
India is staying where it is. Only regional and communal tensions can break it. Hindutvavadi agenda is more likely to play its part.