At what point does he realize that his decisions are bad and he needs supervision?
Why would he ever think any of his thoughts are bad? When would it even occur to him?
He is a billionaire married to a VS supermodel. At this point, he's more likely to squander all his money and make reality TV appearances to make ends meet, than turn Snap around.
I don't think the board has much say. The co-founders have control over all stockholder decisions and even if they were fired (which would only happen if they turned on each other) they would still exercise the same control of stockholder decisions. So I don't think the board really has any leverage...