The key factor is the timing. During the primary week where this product generates income, Google completely screwed me over with no warning and no answers about what's going on. I am of course looking into alternatives, but that takes time, and 3 days from now it'll be too late.
You have no contract with Google though. You're literally siphoning on what is a really low-barrier, dare I say free service.
They didn't screw you over. You chose to use them. You didn't pay them, they're paying you.
If you don't like that arrangement, feel free to join a partner agency that can buy and sell ads for you on the ad exchange or go to a different ad network.
Then, if they do something you don't like, you actually have very real power to compel them to do something.
I don't see how this is ruining your business. A vendor is not playing well with you, just go to another one?