The Nirmankaya is one of the rarest  accomplishments on the spiritual path. Where a Yogi never needs a womb to come in a human form, he simply can create a human body by will.

The word Nirmankaya  is the composition of two words, Nirman+Kaya: Nirman, means to create or to build, and Kaya means body. So Nirmankaya Yogis or say Gurus are expert to take any human form, they need not re-incarnate in a womb.

That’s why some gurus who have left their physical body can come and talk to the people, they are still alive but yet not in the gross physical body, they live in some other plane and help the needy.