The rudder on big jets is purely used to counter asymmetric thrust. It is an extremely powerful flight control and aggressive use can over stress the tail itself. (eg. American Airlines A300 out of JFK).
Also big jets (eg. B777) have inboard flaperons near the wing root and outboard ailerons near the wing tip for roll control. At high speeds and altitude the outboard ailerons are locked out as they would be way more powerful than required. This will also prevent the wings going into a deeper stall when ailerons are used to control roll during a stall.
Finally, jets have a stick shaker to warn pilots when the aircraft is approaching a stall condition and a stick pusher to prevent the aircraft becoming fully stalled. Therefore the ailerons are still effective and safe to use as the aircraft is not fully stalled.
I hope this helps.