In the Vinaya text(Vinaya Pitaka>Culavagga>Bhikkhuni khandaka)
While the Mahapajapati Gotami requested to join the Bhikkhuni Sangha, the Buddha has claimed the Buddha's Sasana will only last for 500 years.
‘‘Sace, ānanda, nālabhissa mātugāmo tathāgatappavedite dhammavinaye agārasmā anagāriyaṃ pabbajjaṃ, ciraṭṭhitikaṃ, ānanda, brahmacariyaṃ abhavissa, vassasahassaṃ saddhammo tiṭṭheyya. Yato ca kho, ānanda, mātugāmo tathāgatappavedite dhammavinaye agārasmā anagāriyaṃ pabbajito, na dāni, ānanda, brahmacariyaṃ ciraṭṭhitikaṃ bhavissati. Pañceva dāni, ānanda, vassasatāni saddhammo ṭhassati.
“O, Ananda!If women not allowed to practice holy life from the home to homelessness under the Dhamma-Vinaya of the Tatagatha, then the true Dhamma would be then lasts long 1000 years. But now, because of the women are allowed to practice holy life from the home to homelessness under the Dhamma-Vinaya of the Tatagatha, then the true Dhamma would only lasts for 500 years."
What about after 500 years?