I should point out that since the guy was the only one who understood his own dialect, it actually fell into disuse when the other person who spoke it died.
I should also point out that language evolves. Like all human behavior, it changes over time. It adapts to fit the needs of the people who use it. Spelling, grammar, and syntax change as cultures shift their priorities from one ideal to another. The form of letters changes. If you fancy yourself a constitutional scholar, you know what ‘regulated’ meant in 1787 and what it means now. A ‘regulator’ is now a thing that controls voltage or pressure. It meant something entirely different in the West in 1875.
It’s funny that academics hoot and holler about evolution every time someone threatens to open a Bible, but when they are confronted with the actual process, they soil themselves in resistance.
It’s also very informative to learn Greek and Hebrew, especially in tracing meanings of terms used over millennia.
It’s amazing the number of scholars who consider ancient languages to be less sophisticated than their own thinking, when those prior generations had far fewer distractions to master the art of expression.
Then again one can succumb to learning....Esperanto.