I believe I may be the person you saw posting here who returned car with 1 key and got GCB.
This was September 2024. Missing key lost 18 months in. We contacted Motability to get a replacement, they refused but said it will not affect GCB and it didn’t, we got full payment, car was otherwise mint, saw it for sale a month later with the dealer describing it as “in stunning condition”.
Seems to me Motability can’t have it both ways, they can’t refuse to provide a replacement under insurance and also penalise you for not having a spare when you hand the car back.
As for keeping 5 years, at the end of the lease, approach Motability and say you don’t have the funds for new car and you need a grant for the AP, but you are happy to keep another two years if they let you. See how quick the grants team extend your lease 😉.
Enyaq EV