Today I had a look on ebay and oh, god! So many cheap used GPUs! Used RX 580 and GTX 1060 at under $100?! Seriously? Looks like miners are selling used GPU as fast as they can!
And mining Ethereum (the most profitable coin to GPU mine for the past months) with 1 RX 580 or GTX 1070 Ti is only earning $1 per day. If electricity cost is $0.12 per kW/h the revenue is less than $0.7 per day. A mining rig of 8 RX 580 or GTX 1070 Ti only earns $5.6 a day...
If mining less profitable coins like monero with higher electricity cost, miners are losing money.
If anyone bought the overpriced GPU last month, it will take 2 years to break even the cost, if mining profitability doesn't continue to drop.
With all these negative factors, mining difficulty continues to rise with even more hashrate joining, altcoin prices continue to drop. Bitmain already released cryptonight ASIC miner and may release ethhash ASIC in the future.
So. Is mining dying now?
It seems to me that you don't understand the specifics of trading on eBay. 100 dollars is only the starting price of GPU. Look at the last day of trading and you will see the real prices. There is a downward trend in prices. But cheaper than 350-400 $ you won't buy the GPU. I do not believe that GPU mining will die. This supports the decentralization of coins and I think in the future a lot of coins will use protection from asic.