Can one receive , in some way, initiation by a Guru who is physically dead even in absence of His/ Her Disciples ( if they exist)?????
Within ISKCON and Gaudyia Math one can find the example of Srila Prabhuapada Bhaktisiddhanta Saraswati who considered himself initiated as a sannyasi by Gaura Kishor Das Babaji as he took sannyasa after a dream near 1918 .
Now not all the Gaudya Vaishnava do accept this procedure and many in Vrindavana reject GM and ISKCON Teachings. Indeed in Sri Isana Nagara’s Advaita Prakasa (8.118-122) it is described how Sita-devi, the consort of Advaita Prabhu, received initiation in a dream from Srila Madhavendra Puri, but that Advaita Prabhu still found it necessary to give her a concrete, audible initiation.
But let us forget ISKCOn peculiar beliefs and imagine the case of a Guru who has not left any official Lineage of Disciples , like Shirdi Sai Baba or Anandamayi Ma.
If I consider such a Person as My Guru how can I receive initiation from Him or Her? Actually I am sure that many holy Gurus did not leave an 'official' Parampara after their Final Samadhi.