I think that in the future the ethereum will switch to a new protocol of work, which excludes mining. If this happens, the owners of equipment for mining will be very unhappy.
No, everyone will just switch to another currency. Nvidia people will go to NeoScrypt coins and Equihash (Zcash) amd AMD guys (RX cards) will jump ship to other Ethash coins.
Nvidia users will have MUCH more flexibility when it comes to mining other coins whereas AMD RX users are more of a one trick pony for Ethash. AMD RX cards can mine other crpyto, but not nearly as good as Nvidia cards.
Thats why ive got Nvidia only, more efficient, better resale and most important, better flexibility.
I bought nvidia for the same reason but I would simply add that nvidia is good for most of the coins, it's only that RX cards are a bit better for some coin. You can make decent money with Nvidia on Ethash.