Yes, Motability will still exist.
EVs will get cheaper as production ramps up. They are still very much a small part of total car production at the moment, but economies of scale will apply.
Motability is a business, but it pays no dividends to its shareholders, the four big banks, so I don’t see why increasing competition will affect it.
i would not be happy to call up a taxi instead of running my own vehicle. I want to go where I want, when I want, at the time I want. If I need to get something I’ve forgotten, I want it now, not when convenient for a taxi company. It would be impossible for taxi firms to cater for the vastly different needs of disabled customers. You only have to look at the enormous number of variations produced to cater for people to realise that it would an impossible task.
As for totally autonomous cars being conducted by the blind, it would take a lot to convince me that it would ever be totally safe. There is no technology that is 100% totally reliable and I certainly don’t see autonomous cars being the exemplar in this respect.