Unless something has changed since 2017 there’s nothing stopping you buying your current car at the end of lease and ordering another one so the PIP holder can continue on Motability and say for instance you sell your old car to a relative or friend. Only pit fall to that is what Motability ask for the car is the same like for like price you’d pay at a franchise dealer forecourt without any possibility of doing a haggle on the price.
I did it with my last car but that’s another long story in the wonderful World of the DLA to PIP transitioning but end of story is I bought my Motability car then rejoined the scheme 6 month later.