I wouldn't go back, regardless of salary offer, unless I didn't have any other jobs lined up. If I'm not employed than any job (even a bad one) beats being unemployed. But if I was employed, I wouldn't go back to a job where they laid me off for stupid reasons, no matter how much money they offered.

I guess the crux of the issue is that there's no guarantee that the company would not find a different, equally harebrained, reason to lay GP off.

There's no guarantee in any job that you won't be laid off.

True, but if you already know that a given company tends to fire on a whim, you'd be excused to feel a little bit distrustful.

For how long?