In the [Parable Of The Skillful Physician And His Sick Children], the physician-father of course represents the Buddha, and his supposed death is like the Buddha’s entry into nirvana. In reality, in the view of the Lotus Sutra, the universal Buddha, the loving father of the world who is working to save all from suffering, has not and will not pass away. He pretends to pass away only in order to get people to be more responsible for their own lives. This is a good example of how the sutra takes what is a basically negative notion, nirvana, and turns it into a world-affirmative one.
A Buddhist Kaleidoscope; Gene Reeves, The Lotus Sutra as Radically World-affirming, Page 183