That could definitely help. However, while I don't have the numbers, I'd expect that the required labor to disconnect them all would vastly exceed the 24-72 hour warning time.

Also, this would mean proactively shutting down the entire grid for days, at the first warning, then requiring days to restore power. So one warning would require a full week of zero power for the continent, and (I expect) saving only part of the grid.

But yeah, putting in some planning to do that would be a smart idea.