I predict miners will need at least 6 months of no profits before we start seeing any meaningful hashrate drop, and even that will depend on how efficient the F3 turns out. If the F3 is very efficient, difficulty will never recover and GPU miners will be toast as no other coin(s) will be able to adsorb all the hashrate and remain profitable.
The F3 could easily drive people out of ETH and into EOS or other similar coins. The Eth devs need to start forking as participation is what really drives adoption. Centralized shit is just that, shit. It has gone that way everywhere it's been tried (I'm not just talking crypto).