Deal will be signed by the Central govt. of India and Bangladesh, West Bengal is legally not a party to the deal. Your central govt. is not bound to ask the West Bengal govt. for approval and can go ahead with the deal, but is still not doing so. I wonder how long India will keep it hanging, especially after this Doklam crisis, you just can't afford to have any more enemies in the neighborhood.
No Central government in their right mind will sign a deal unacceptable to one of our states over a neighbor. West Bengal has to sign off on the deal. At least they cannot object. If I have a choice between pleasing a neighbor and our own citizens my choice is clear.