We don't need lots of power consumption to run bitcoin network, we just need some miners and nodes who has good hardware and internet connection.
For instance, block times are way too long for instant transactions. The blockchain is getting too bloated. It's using up energy inefficiently.
One day, bitcoin will fall.
Instant transactions can happen if merchants accept zero confirmation.
Also, blockchain size problem will be solved in future and there's no direct connection between blockchain and energy inefficiently.
yes, they will have transaction fees.
and if think that's not enough, just remember about supply x demand. with less/zero bitcoins been generated every day just a few satoshis will worth much.
I think that won't be problem if bitcoin is commonly used by everyone which means there'd be lots of transaction and bitcoin would be very valuable.