It will be fee based. Right now they get 12.5 btc for the block and 3-8 btc for the fee so block rewards are sometimes 21 btc total.

This will drop to 3-10 btc in fees. Tech and power consumption will be very minor relative to today when this happens.

Also, this is why bitcoin cash roadmap is superior. Unlimited transactions with cent fees each will add up to more than a 1mb fee Only block.

If everything held constant. Btc would die and bch will live due to miners switching over.

2k transactions at $10 fee each = $20k usd. This is btc

Bch Be 100k transactions at 21 cents each = $21k usd