Um... If you've choked someone out, they are, by definition, close to dying. You've cut off the blood flow to their brain, and they *will* die unless you let go in a timely manner.
Which is not to say that chokes shouldn't be practiced, just that one should respect the seriousness of what one is doing.
You haven't actually cut off blood supply to the brain, you've merely reduced it. You reduce the amount of blood and therefore oxygen the brain receives. But the majority of the blood flow (and oxygen) carries on unimpeded. There is a rather large safety margin, in terms of time, between the person passing out, and brain damage setting in. Of course you let go as soon as they nod off anyway, just to be safe, if you even take the technique that far.