that will not be a real problem because "free energy" miners would have to amortize their investment and coins would have minimum value imposed by them, the real problem would be, and maybe critics will find intrinsic value of bitcoin too, when we manage to create matter from energy with methods within reach for everyone.
I don't want to go too sci-fy here but recent discoveries made me believe we may have star-trek "replicators" more close than we thought... link
Imagine a world, 50 years from now, in which everyone has it's personal "replicator" just the size of a microwave oven where he can push some buttons and replicate any material thing you can think of like food, raw metals, tools, you name it. In that case what would you use as store of value ? Could bitcoin be our latinum ?