firm needs to pay his share in firm and Goodwill to the legal heirs of the deceased.
if you were the only two partner's of the firm then the firm wud stand to be dissolved since at least 2 person are required to carry on the firm .so the existing PAN GST of the firm needs to be surrendered.
However if you admit any legal heir of the deceased and make the necessary changes in the p'ship deed and get it registered then the existing firm can continue provided that there is a clause in the deed that on death of existing partners the legal heirs would be admitted as partners in the firm.