I think it depends on how we come about the energy cost decreasing, if we have nuclear fission and it drives energy costs down it just encourages more people to participate in the network and increases security as more people are mining at cheaper costs

The price would then have to find a equilibrium between the cost to create and the need to cover those costs

If it's only bitcoin that now takes up no energy, I don't see it surviving as what does it tether itself too as a real world expense to create? The whole point of hard money is that it takes a cost to produce, a cost we could choose to produce bitcoin or produce something with a higher stock to flow than bitcoin