I don't know if this can help at all for you, jppe. But since that workplace I went through, Machka has done an incredible looking up of stuff about brain injury. She found this person's story in particular which illustrate that, as a cyclist who suffers brain injury, there is long-term recovery possible:
https://www.brainline.org/blog/getting-back-bike
Also, there was recent news that a woman in the United Arabs Emirates woke after 27-plus years in a coma which resulted from a vehicle accident.