It would only take a little longer than a decade 😜
Discussion
I doubt that...
A human can do what, 1 hash / day, and there's a lot of hashes in 100s of exahash...
How long did it take to go from basically zero difficulty to where we are now? ;)
It's more like, how long would it take you to find 2016 blocks of the current high difficulty on pen an paper?
Then there's the first difficulty adjustment, down by maximum a factor of 4.
And again, how long would it take to find 2016 blocks of this still damn high difficulty.
Then there's the second difficulty adjustment, down by maximum a factor of 4.
There will be many adjustments before it's back down to genesis difficulty, but it would take decades, centuries?
Plenty of time to re-invent generators and semi-conductors! 😂