For one, if a formal declaration of war happens, then most ships would like to stay outside the war zone for obvious reasons that these ships are not owned by govts but private companies who would not like to place their property or personnel in harms way. So nothing much will happen other than they companies lodging a strong protest with Ministry of External affairs India. The govt can't so much either than lodge a protest or call a session in UN, which is a long drawn process.
I agree with you that subs does provides a strike capability and if war commences than subs will be the first to be launched into the seas 'cause they won't like being caught in shallow waters
But then obviously we will have the P-8i hunting for these subs and since BD airforce will not have air superiority over BoB airspace there is not much they can do to stop these anti-sub sorties. So just having them won't ensure a blockade won't happen, it will be an annoyance for IN at best. Unless, BD also acquire sea launched harpoons for them too, in which case these subs will become a priority target and IN would like to launch sorties to take them out.
And... This is precisely the reason, I wrote a comment before that as a 'sovereign nation' if BD want's to buy subs, they can, if they feel more secure and if subs fulfill their defense needs, they should go for it.
Besides, I feel other people (Indians and BDs both) are plain overreacting over something which is a good 10-12 years away
