He could buy himself an income protection policy from Friends Provident. basically, if you are off sick from work it replaces your income. MTBing is not classified as a dangerous sport. so the premium would be calculated based on the risk associated with his job & his historic health record.
It can be a bit of a shit to underwrite involving doctor reports (paid for by the insurer) and a fair amount of waiting. but if you are self-employed and like to take risks I don’t think you can beat it as a catch all “pay the mortgage & bills” solution for those of us who can’t afford to be off work for long periods.
And while I understand it doesn’t help for now, it might give him the confidence to go back to riding.
I say this in 2 guises:
1 as someone who is self employed & had 6 months off work with a bike related broken neck &
2 as someone who used to give advice on this stuff.
I can point you toward other resources who can tell you if this would suit your circumstances. Or find your own IFA.