The quote “to become immortal and then die” stands correct for human beings who indulging in spirituality finally succeeded reaching state of enlightenment followed by moksha salvation.
Mahavira, Gautama Buddha even Jesus Christ and Prophet Mohammed gained immortality in their lifetime but not physically. All these man gods became immortal through their immortal teachings which are not only available but also practical even in present times.
Initially all these enlightened souls became immortal as they gave to mankind pearls of wisdom contained in their teachings. And when these enlightened souls left their mortal frame, they physically died forever. In reality enlightened souls never die but live through teachings.
So is the case with Adi Shankaracharya, Sri Ramakrishna Paramhansa and Maharshi Ramana.
It is following teachings of all these enlightened souls I finally succeeded in reaching state of self realization, god realization 37 years of age. This is my last manifestation on mother earth. Moment I leave my mortal frame I shall attain moksha salvation.