Take overs, mergers, bankruptcy, it all happens more than you think.
It depends upon the way the take-over was structured as to whether or not your sponsor still exists and whose payroll you are carried on. But in the most common scenario, when your sponsor is swallowed into a new entity, or otherwise ceases to exist, you're stuffed. The new entity has to sponsor you. If they don't report it, then they AND you are stuffed.
If it's the same job (etc), they can avoid having to start at square 1 and start at square 2 instead. But that's all you get...