It's already owned by the same few people who already own everything else. And of course there is no switch-off, unless they abandon it for lack of profitability. When we reach 50% unemployment, everyone defaults on their loans and there is nobody left to buy all the goods and services, and there are no taxes left to collect, the whole economic and political structure collapses, because no provision has been made to change gradually from a debt/profit driven organization to whatever the next thing is.
That's not likely to happen, though. Certainly, there will be riots long before then, bombings and burning of automated factories, maybe derailment of driverless freight trains, etc. Police will have to gas and shoot protesters, jail their leaders and all the usual rigamarole when the plebes get too restless. Maybe it will peter out in a cascade of financial and civil crises; maybe someone can start another war of distraction (though that one's wearing pretty transparent and can much too easily escalate to total annihilation) and deploy all the artificially intelligent weapons.
No off-switch; no public domain; no contingency plans. We just have to hope AI gets smarter than we are and takes over the helm before we run it into the iceberg.