Write at least one coin that will give a profit if at least a third of the current Ethereum miners continue mining.
The most expensive video cards will now give such a profit, which is given by some of the weakest video cards in mining, for example, the RX 470.
Absolutely true. This has been discussed many times on this forum. ETH comprises 95% of the block reward income available to GPU rigs. After PoS, the revenue we get will be just 5% of what it used to be at first, until network hashrate collapses to a reasonable level. At that point, GPUs will become very cheap and it will make sense to build a rig again.
The losers will be those who bought video cards at inflated prices but haven't reaped inflated 2021 profits.