Joss, I think the page you quote from has been superceeded by introduction of the ‘Stopped Allowance Support Payment’ – from the ‘If things change’ page on Motability’s website:
If your allowance ends during your lease
If your allowance ends during your lease, you will no longer be eligible for the Motability scheme and we will support you through the process of handing your car back.You may be eligible for a £1000 stopped allowance support payment if your return the car in a good condition to your dealer within our given timescales. Depending on your individual situation you will have up to eight weeks from your allowance payments ending to return the car. If you receive a stopped allowance support payment, you will not be eligible for a pro-rata Good Condition Bonus, but any Advance Payment you have paid will be returned to you on a pro-rata basis.
https://www.motability.co.uk/your-lease/car/if-things-change/