It is entirely hypothetical unless another member has done this.
However, Motability are very careful to leave any insurance problems for the customer to deal directly with Direct Line. I fail to think why anyone would be treated any differently because they are a Motability customer.
But willful damage to the car, no doubt if Direct Line washes their hands of the claim, then the customer would be liable for the full cost of the vehicle.
No doubt that scenario will be in the agreement document you signed on the vehicle lease.