Surely this is a lose lose situation. Even if Motability decided to allow a car to be purchased at lease end to keep the peace, or were forced to do so due to contractual obligations, they have every right to set the price and could inflate it to make a point:
“Hey, what’s the top book price for this car?”
“OK then, lets stick another five grand onto that and offer at that price!!”
Not saying they would, but they could!