What's the canonical definition of end of the buddha sāsana?

Question

I was under the impression that the end of buddha sāsana occurs when noble eight-fold path(and the dhamma practitioners) disappear form all the realms including Śuddhāvāsa where only anāgāmins live. This contradicts with Ghatikara sutta. It consists of a lord buddha's conversion with an anāgāmi brahma Ghatikara form Kashyapa buddha sāsana. That means at least anāgāmins and arahants from previous buddhas might still live in arupa brahma realms.

Did anyone come across a canonical reference for end of buddha sāsana?

Answer 1

I was under the impression that the end of buddha sāsana occurs when noble eight-fold path(and the dhamma practitioners) disappear form all the realms including Śuddhāvāsa where only anāgāmins live.

Imagine a school where only music prodigies or math prodigies attend, one would never have to worry about the decay of the school's reputation. The Pure Abodes are also like that. Since it's a realm where Non-Returners reside, it'll never face the problem of Dhamma decline there. Earthlings on the other hands, are much more inclined towards sensual pleasures and many other unwholesome deeds. It's the Dhamma on earth that's facing a serious danger of going into decline.

In SN 20.7, although the Buddha didn't give an exact number on the life span of the Dhamma, He did give the clear sign and cause to its disappearance:

"...In the same way, in the course of the future there will be monks who won't listen when discourses that are words of the Tathagata — deep, deep in their meaning, transcendent, connected with emptiness — are being recited. They won't lend ear, won't set their hearts on knowing them, won't regard these teachings as worth grasping or mastering. But they will listen when discourses that are literary works — the works of poets, elegant in sound, elegant in rhetoric, the work of outsiders, words of disciples — are recited. They will lend ear and set their hearts on knowing them. They will regard these teachings as worth grasping & mastering.

"In this way the disappearance of the discourses that are words of the Tathagata — deep, deep in their meaning, transcendent, connected with emptiness — will come about.

Answer 2

The suttas say that the Buddha sasana will last five thousand years (at the midpoint of which we are now, incidentally), followed (about 4600 CE) by a long dark age during which dharma is completely forgotten as humanity continues to degenerate and the age of degeneration reaches its nadir.

At this point humanity will enter an evolutionary arc and pateccabuddhas will arise but not teach dharma till the appearance of Lord Metteyya, the Fifth Buddha of the current age, who will initiate a new dharma sasana in the far distant future (most estimates vary from tens of thousands to millions of years).

I have always found it interesting that humanity enters an evolutionary arc automatically as it were without a corresponding Buddha appearing till it is near its zenith, described as a golden age including advanced scientific and technical knowledge and a large terrestrial population and great cities, which contradicts the common view that buddhas only appear at the nadir of the age.

Answer 3

This answer won't be very helpful but many of the sutras are meant to be helpful expedients. If you take them too seriously you will emerge with this problem. (The lotus sutra contains the least expedients of them all, as far as I recall.) Even if I knew where this is referenced, the numbers given would be shaky and subject to interpretation. For example it says that the average lifespan of a human being varies between 10 and 10^140 years according to wikipedia.

I wish you good luck but it seems unlikely that a satisfactory answer can be found and even if one was found, there would probably be more than one text claiming more contradictory figures.