The only viable,, sustainable and peaceful solution to the Kashmir issue is reunification of India and Pakistan and formation of a new Akhand Bharat or Hindustan or United India or whatever you may call it, although this does not seem imminent anytime soon.
Similarly, outstanding issues between Bangladesh and India like Land Boundary Agreement and Teesta Settlement can also be permanently settled through reunification and creation of a Greater Bengal state as it was in the past.
Another alternative to political reunification is a stronger political union between SAARC (South Asian Association for Regional Cooperation) nations:
The formation of the European Union united UK, France, Germany, Austria and other arch enemies. There is no reason to believe that this is not possible for SAARC nations. The intense nationalism/jingoism/fanatical patriotism of the European countries in the past was way more than what Indians and Pakistanis feel for their motherland today. Still, they found a way to permanently settle their centuries-long disputes. The key is political will. Unfortunately, the European nations acquired such wisdom only after understanding the futility of war after the utter mass annihilation and destruction caused by the 2nd World War. France, Britain and Germany used to be superpowers before the two great wars. After that, they were reduced to the status of developing countries and United States of America took centre stage on the world stage.
Mahatma Gandhi had said that war is the failure of man as a thinking animal.
It would be a dream come true if SAARC becomes as strong a grouping as the EU with all its attendant benefits: free trade, free movement, collective defence security, single currency, international amity, etc.
The great Indian yogi, Sri Aurobindo was a proponent of reunification of the Indian subcontinent.
Wish this miracle could take place in my lifetime. Jai Hind.