[fulafel]

As a nuance, the grid falling over would not yet result from too much demand, absent other snafus. Rather you have rolling blackouts when loads get disconnected by the grid operator, or if there are failures in implementing those in a orderly way, less orderly blackouts for parts of the grid. These kinds of managed blackouts are common in some parts of the world, eg South Africa, the recent Texas situation, etc.

The frequency of the system is a clear signal about the demand/load match, and if it starts to drop more below some threshold of deviation, loads get disconnected from grid branches.

Of course there can be "interesting times" leading to cascading processes in the multiple interacting automatic failsafes, you can read up on post mortems of grid failures about what kinds of things can go wrong, eg https://en.wikipedia.org/wiki/Northeast_blackout_of_2003#Seq... .. which is why really want to preemptively do the controlled rolling blackouts instead.

The grid falling over would result in a harder, more uncertain and lengthy "black start" process, since plants need power to restart. See eg https://practical.engineering/blog/2022/12/5/what-is-a-black...