>If all grocery stores and restaurants run out of food for a long enough time people will starve. This isn't a problem in practice though...

I fail to see how this isn't a problem? Grid failures happen? So do wars and natural disasters which can cause grids and supply chains to fail.

That is short hand. The problem exists of course, but it is improbable that it will actually occur in our lifetimes. An asteroid could slam into the earth or a gamma ray burst could sanitize the planet of all life. We could also experience nuclear war. These are problems that exist, yet we all just blissfully go on about our lives, b/c there is basically nothing that can be done to stop these things if they do happen and they likely won't. Basically we should only worry about these problems in so much as we as a species are able to actually do something about them.

If they are at small scale then it's fine.

If it's at large scale then millions die of starvation.