There is a glimmer of hope for those who are within the last 3 months of their existing lease and have already got a confirmed order in the system. This in the FAQ on Motability site:
I have placed an application, will the handover of my car go ahead?
Following the Government’s latest announcement, the network of dealerships who help to supply the Scheme has now been forced to closed. If you are currently already a customer with a car on the Scheme your lease will automatically be extended for a further six months and you will also automatically receive a Certificate of Motor Insurance or a temporary cover note from RSA Motability (RSAM) covering this six-month period.  If Government advice changes and your dealership re-opens earlier than this, then you can contact your dealer at this time to arrange an earlier handover.