Just an educated guess, but I would think that any supplemental carbs would be beneficial because it helps slow down your body from cannibalizing its own protein and lean tissues to convert into glucose.

I forgot where I read that even emaciated people who die of starvation still have some fat stores in their bodies. If you haven't succumbed to disease or infection by then, I think your body simply has basically digested so much of its own "machinery" that it finally shuts down rather than completely running out calories. But that's the uber extreme case there.

The transition from having a metabolism that uses primarily ketones to glucose probably requires a good amount of carbs at one time to shift significantly. But I would think that if your body is already adapted to ketosis, it's going to be easier to transition back even after a significant hit of sugary berries anyway. I suppose that a devoted adherent to something like the Atkins diet would have better firsthand comments on how this transition back and forth actually feels to a person and how quickly it can happen once you're adapted.