I think, when the world's electricity supply is still large, and has reserves from every source, the world's electricity will be able to handle bitcoin.
in addition, the development of electricity is never stopped, the innovation of electrical energy from various sources has always been used to save world electricity, such as hydroelectric power, solar power, waste power, and steam power.
The world does not have "reserves" of electrical energy, since on large scale electricity cannot be stored. It must be produced just when it's needed. So if the Bitcoin network is consuming X energy, that quantity has to be produced in real time, with all the implications of that.