That's assuming the BCH chain lasts that long. Bitcoin itself has only existed about 10 years or so. Who can say what will happen in the next 20-40?
Even if BCH chain were to completely die, I think some people will still keep a copy of it around forever. Right now you can store the entire chain on a $20 drive.
Reviving it on another POW would also be very easy
So, if it dies, it's cheap to keep, and if it lives and survives, that will be irrelevant. Huh.
