Well thats the key point , why would it deteriorate? I dont think India will allow any foreign troop movement on its soil or water. Thats not even fiction. India wont even allow russia or US for that matter of fact. India is a power on its own which can say no , unlike pakistan which capitulated on afghanistan.
Which country do you think bangladesh might get into war (other than India & myanmar)? Even during heights of khaleda's ant-India govt when BD was providing arms & safe havens to terrorist groups India did not attack bangladesh.
There will be strings in security alliance like for India & USA. But not for India & BD , it will be like US & Canada. Any damage to one of them , will impact other. Each side will be vary of that and not allow things to go out of control. The only question , is the subcontinent ready for that?
US & Canada are smart countries the relationship between them is bereft of pettiness that is typical to subcontinent. By having such an arrangement they are actually saving ton of money and also better economic benefits to its citizen.