In fact, Bitcoin lost around 40% of its value after the Bitcoin Cash fork emerged. At that time, it wasn’t immediately clear which chain would actually keep the ‘Bitcoin’ name.
Therefore, there’s no certainty that miners would back a new developer fork aimed at quantum resistance — they might prefer to stay on the original chain.
~snip~
40% you say? BCH absolute ATH was December 20, 2017 - price $4355, while at the same time the BTC price was around $17700 and it was actually a great year for BTC. Maybe some wondered who would
"win", but I think everyone knew that Bitcoin would remain Bitcoin because everything else is and will be just bad copies.
Miners are mostly after profit, so they will mine what brings in more profit. After all, someone is still mining BCH today, right?