I think with lightning network and anything else that will put on top of that the transactions will be fine even without the electricity costs. I don't know how miners will profit from it in the end because I am not a miner and I haven't dealt with the operations of a mining place however I know how it will affect the users since I am a user.
I have been looking into getting a ledger nano just so I will be capable of sending and receiving on the best possible ways, that way I can pay less transactions via lightning network when available or segwit right now. Which means for the customers the future is not for electricity costs or some better mining equipment or something, the future is better core development codes for bitcoin itself which could make it cheaper.
If miners will not get a profit, they will stop mining.
If this happens there are two things that will follow
- hashrate will drop, the network will be less secure, anyone could buy the mountains of scrap mining gear that will be sold at scrap metal prices and guess what they might do with it
- if miners really stop completely (which is an impossible scenario since you will need only a simple computer to mine a block once difficulty will die down) there will be no more transactions, no more opening and closing channels in the LN ..no bitcoin whatsoever. So, you as a user with your ledger you will be just as the rest of us...f****!