We sometimes practice the rudder hardover scenario (737) even though all aicraft in service have been modified to prevent this.
I would say that an average pilot should be able to fly the aircraft to the runway - as long as you keep high speed, with differential thrust, the aircraft is still somewhat controllable. The most difficult part of this exercise is to keep the aircraft on the runway during the rollout - I've seen it done using more-than-idle forward thrust on one engine and full reverse on the other and then slowly reducing both. Nevertheless, as said, this is not applicable to light aircraft with mechanical (cable/pushrods) flight controls.
What I would suggest however for advanced training is to show people how to make a traffic pattern (from beginning of takeoff roll to stop after landing) in a C172 with only rudder, throttle and elevator trim. It's really an eye opener and makes you more prepared in the event of control surface problems...