Matsya Purana — Procedure for Going to Prayaga and the Greatness of the Ganga
यावदस्थीनि गङ्गायां तिष्ठन्ति हि शरीरिणः तावद्वर्षसहस्राणि स्वर्गलोके महीयते //
yāvadasthīni gaṅgāyāṃ tiṣṭhanti hi śarīriṇaḥ tāvadvarṣasahasrāṇi svargaloke mahīyate //
So long as a person’s bones remain in the Gaṅgā, for that many thousands of years that embodied being is honored and exalted in the world of heaven.
It does not address Pralaya; it teaches the post-death spiritual merit (puṇya) gained when one’s bones remain in the Gaṅgā, resulting in honor in Svarga.
It supports the gṛhastha duty of performing antyeṣṭi and śrāddha-related rites—especially asthi-visarjana in sacred waters—ensuring welfare of the departed and accruing religious merit.
Ritually, it highlights the efficacy of asthi-visarjana (immersion of bones/ashes) in the Gaṅgā; no Vāstu or temple-architecture rule is stated in this verse.