From what I understand, ETH issuance rate is going to go down after the merge.
In your hypothetical, demand stays the same. The supply stays the same, too - because the gold mines are still limited to the same amount of gold they get out of the ground.
So long as the amount of gold is mined unchanged, the fact that the processing is cheaper makes the mine more profitable but doesn’t change the price of gold.
But this is not the case, the 'mined' ETH will come from proof of stake. Some people with more than 32 ETH and an online server will keep the engines rolling and get 5% in return for their service.
The less power is because the electricity is used for serving instead of mining.