In theory it's the difficulty that should settle such that the cost of the electricity to make them is approximately equal to their value.
So, for example, when generation switches from 50 per block to 25 per block, the value will remain the same and it will simply become uneconomic to mine. As miners leave the network, the difficulty will automatically reduce until equilibrium is reached again. (In theory. In practice, the time lag until the difficulty changes could make this an unstable feedback loop rather than stable).
So, for example, when generation switches from 50 per block to 25 per block, the value will remain the same and it will simply become uneconomic to mine. As miners leave the network, the difficulty will automatically reduce until equilibrium is reached again. (In theory. In practice, the time lag until the difficulty changes could make this an unstable feedback loop rather than stable).