"I don't know" is the more honest and accurate statement in many cases. I generally use it, but in this case my view is that the cost of energy ultimately plummets to nothing as energy becomes abundant. At that point energy's primary use becomes to secure the Bitcoin network and our own savings, then when the block reward won't be replaced by transaction fees as the reward will be users simply helping to secure the network.

Users will possibly subsidize the network to secure their own savings. In hundreds of years when the block reward drops to zero the world will look completely different. We may not even need Bitcoin at that point, perhaps Bitcoin is transitory to whatever the future ends up being.

As for the last point, it's hard to say what we will use to measure the ever growing spending power of Satoshis in the future. The dollar and cents will only be useful for so long until Bitcoin becomes the dominant money globally. Perhaps we'll measure value in Gold oz, I don't know. But we're at least a decade away from the downfall of the dollar IMO.