We would have to back quite a ways, and roll back the chain, that's unpossible (transactions, money has moved, content would be lost, it cannot just be flipped like a switch once the train is too far from the station. However ,it would have been possible, last week... like it was the week before. I know, because I'm a witness who had to do just that overnight and has been up all week sleepless, shepherding patches and confused users all over the platform, ever since.