Nobody is "Not Replacable" in this world. Yes for some situation you may have "established' alternative, in other cases there may not be any proven alternatives, but that doesn't mean there is no no alternatives.... they may be risky, there there are alternatives with unknown factors... unless you try...you will never know.
If bangladesh team doesn't have any plan B (for captaincy) in their sleeve, then who is to be blamed? Of-cource its BCB to blame. Why they have a VC in the team then? And how they are using that position grooming Captaincy as Plan-B, that have to be questioned.
"When Soumya Sarkar shines, Bangladesh smiles!"