My Qashqai is seven and half years old. Full service history with a Nissan dealership. last service only 6 months ago, and has done approx 53k miles. About five weeks ago, when driving I heard a noise from under the car and then the oil and battery light came on.

The dealership said,the auxiliary belt had failed and the frayed strands from the belt have caught up in the crankshaft pulley and the timing belt teeth. Saying this caused the belt to jump teeth and disturb the timing of the engine. Resulted in engine seizure and they say the my car now needs a replacement engine.

Is it possible for them to diagnoses this when they haven't strip the engine? And should I request this? Although there is a cost of £360 I believe for this stripping engine.
The dealership was quoted me over 5k for a reconditioned engine. As you'll appreciate this is not desirable option.