I don't think there will fewer miners. I think it's more likely that the price of Bitcoin would increase.

There a lot of very large mining operations that cannot afford to scale down, and they won't sell their mined Bitcoin at a loss. If there are fewer transaction fees, this smaller amount of BTC would have to pay for all of the electricity that was used to mine a block.

Maybe everything would change if the mining operations started to run their own power plants that use free and renewable energy. They could buy some land next to a river and set up a hydroelectric power generator. That would just be a capital cost, and if you do it right, then it could cost very little to maintain. The operational cost would be maintenance, the internet bill, and fixing/replacing broken miners. Even if the mining doesn't work out, I've just been reading about some people who do this and sell excess power to their power company.

The price will not be able to increase to the point that the mining block bitcoin reward itself will incentivize miners. As the mining block reward approaches zero, transaction fees will be the only way to incentivize miners. Since there will be fewer transactions, transactions won't have to provide a large fee just in order to get the transaction in the next block. The reduced transaction revenue will cause many miners to leave the network. Fewer miners will mean easier difficulty. This phenomenon stabilizes when mining is still profitable at the lower transaction revenue level.