On the contrary I believe that may declaratory decree is not applicable as the plaintiff has not been denied his/her right by the defendant. Further the adjudication process before the Collector is different to registration before the Directorate of Registrar.
In case there isn't any sale deed, the querist need to engage an Advocate for its drafting and ask the other partner who is still alive to do the registration. If the partnership was registered, the libilities or obligations of the partners did not extinguished. If your request to do the registration does not materialize, you may file petition before the Court for mandatory injunction under the Specific Relief Act.
As your matter is already running late, any further late would invite Doctrine of Acquiesce, thereby the Court will be more reluctant to grant you relief or invoking its discretionary power.