You can extend the lease for 5 years, So i would imagine if nothing is suitable right now, they would extend it till sept 2023.
As kezo says best to phone and talk to them.
Another thing to remember is that you will get a one off new car payment of £250 on top of any gcb but after you get the next car, so you have to put up any ap 1st which for some is not easy right now.
Recently i just left the scheme and got my own car and i guess that might be the option for you if you need a diesel and nothing is available on the scheme when that time comes even if they do extend.
I can see the same issue moving forward for many and having to pick something else, hybrids will still be sold till 2035 but i see many will just make ev’s.
I don’t know why you cannot search via mpg anymore so have to look at all cars to see the mpg and which petrol maybe a good options for you over others available.
I did a search upt0 1k ap / no small cars/ under 25/ and was only 14 cars https://tinyurl.com/5sjm3bjy
just over 1k is the HYUNDAI KONA ELECTRIC HATCHBACK 150KW PREMIUM 64KWH 5DR AUTO if you have a driveway then an ev might work for you depends on the mileage you need to do, but has a Range of 484 km or (300 miles) where as the cheaper version has only around 189 miles range.