The word rta did not survive; the idea did, twice over. Within India its work passed to dharma, a younger word built on the root dhr, to uphold. The transfer can be watched happening: in the later Vedic literature dharman appears alongside rta as the upholding of the ordinances, and by the time of the dharmasutras and the epics, dharma has absorbed the whole territory, cosmic regularity, ritual correctness and moral obligation, while adding what rta never quite had, a jurisprudence: duties differentiated by station, stage of life and circumstance.
When the Buddhists made dhamma the name of their teaching and the Hindus made dharma the name of right order itself, the old Vedic intuition was traveling under new papers. The second survival ran west. Rta's exact cognate is the Avestan asha, and the pairing is one of the cleanest results in the comparative study of religion: two traditions, Vedic and Zoroastrian, separated before either wrote anything down, each carrying the same inherited word for enacted truth as the spine of its religion, Varuna guarding the one, Ahura Mazda championing the other, each opposing it to a matching word for the lie. Whatever the common Indo-Iranian religion was, its center is visible here. Scholars have long set rta, asha, the Egyptian ma'at and the Chinese dao side by side as the great cosmic-order concepts; the family resemblance is real, but only rta and asha are actual kin.