No one really mines ETH... There are way more profitable coins to mine. I dont see your correlation with GPU Mining Dying....
I got my numbers wrong last time so lets try again. Lets convert nethash to number of gpus, for simplicitys sake for example rx470
Some most popular coins amount gpu-miners - zcash, monero, etc
Zcash Nethash 335 Mh/s Hashrate per gpu 260 h/s Number of rx470 eqivalent gpus 1,300,000
Monero Nethash 250 Mh/s Hashrate per gpu 660 h/s Number of rx470 eqivalent gpus 380,000
ETC Nethash 8 Th/s Hashrate per gpu 26 Mh/s Number of rx470 eqivalent gpus 307,000
And ETH: Nethash 100 Th/s Hashrate per gpu 26 Mh/s Number of rx470 eqivalent gpus 3,850,000
So, claim that noone is mining ETH isnt exactly true.
There are a lot more algos... Lyra2v2 has the equivalent of ~800,000 pcs RX470 in hash-power on WhatToMine (adding up everything except Nicehash).
Go over to ZPOOL and you'll see other popular algos like SIB, Blake2s, Xevan, X17, Skein, Timetravel, etc, etc.
I believe soaking up the GPUs from ETH can be done... although I would bet a lot of them would just get sold off since the AMD cards aren't terribly strong on many of the other algos and AMD is the majority of ETH mining.
Sure... there is risk that ROI will go down, obviously, but my operation could take a 10x reduction in profit before it became completely useless (e.g. Power costs more than profit).