Tapasya for a fallen yogi – BKS Iyengar
Patanjali warns that even such exalted yogis are not beyond all danger of relapse.
…Inattention, carelessness, or pride in one’s achievement await opportunity to return, and fissure the consciousness. In this loss of concentration, old thoughts and habits may re-emerge to disturb the harmony of kaivalya.
If this takes place, the yogi has no alternative but to resume his purificatory struggle in the same way as less evolved people combat their own grosser afflictions.
~ BKS Iyengar (Light on the Yoga Sutras of Patanjali)