Manikar Das Brahmachari he did not leave iskcon. but Prabhupada's mercy has left him.
aprāṇasyeva dehasya
maṇḍanaṁ loka-rañjanam

HDG's PhD is like the ornament on a dead body. Such ornaments simply serve the concocted pleasures of the general populace. But they do not attract the mercy of Prabhupada. Hari-bhakti-sudhodaya (3.11)