...and you guys are not even taking into account that there will be GTX 11 generation next year. This will kill resell value and make your hashrate not competitive against GDDR6 etc.
Gamers will still buy GTX 10 cards. The market will determine their value on the secondary market, and that price will fluctuate depending on how many miners are dumping to upgrade or to get out of mining completely. Heck, gamers are still buying GTX 900 cards if the price is right, and they are up to 2 years old at this point.