"Since A is not anymore, how to proceed in getting a share to the nominee. "
The nominee is mere trustee, a hand to recieve the proceeds and handover to the legal heirs.
Nomination does not prevail upon succession.
Succession is as per personal law applicable to owner.
If, Nominee is not a successor/legal heir, then nominee has NO share.
If Nomination was valid and registered and persists till date of death, then nominee can submit claim for payment to Bank.
Bank can discharge its rsponsibility by making the payment to nominee.....................until or unless there is stay by court of law.