According to Osho, after the seventh plane (nirvana) no one returns; rebirth ends. Yet a realized one may, from the fifth body, consciously leave his second (etheric), third (astral), and fourth (mental) bodies as energy-fields in space. When a prepared person appears, these subtle bodies enter him, transmitting the Buddha’s accumulated experience—thus “Maitreya” manifests, not as the same soul, but as preserved consciousness-vibrations.
You can’t come back after nirvana, but a master can leave subtle energies that later enter a ready person, making the master’s wisdom live again.