Good day, Rob. I am very sorry to hear about your problem. It's disappointing, to say the least, to have something like that happen if you are dedicated to your musical instrument, regardless of whether you are a professional musician or not (I'm not a professional musician either).
I assume you meant spraining your wrist, especially given the rest of your description, which sounds like some of the carpal bones got dislocated due to complete rupture of some of the ligaments (had you actually immobilised the wrist following the accident?). I had a somewhat similar experience as a child (I had 2 fingers sprained in addition to the wrist on my left hand). I personally recommend finding a good chiropractor first, before attempting anything more "invasive", that's what's helped me (and fairly quickly as well: within only 3 sessions).
Other than that, physiotherapy... And a physiotherapist will be able to refer you to a doctor who specialises in sports-related injuries (that's the secret with problems like that when it comes to music: pretend you're an athlete and look for professionals an athlete would try to find if they had a similar issue).
You could also try switching to a lap guitar. Having the fretboard aligned horizontally should theoretically take some pressure off your wrists.
If none of the above helps, the last resort I can personally think of (because ligaments don't really "heal" except through scar tissue and only in certain areas of the body) before attempting surgery is to switch strumming hands. Assuming you're right-handed, just switch to strumming with your left.
Unfortunately, I can't recommend much in terms of exercise, because I haven't had any mobility (or finger-bending) issues myself. Except a small rubber band for the hand (if you can find one in your country), which is a rubber ring that you place into the palm of your hand and then "squeeze" with your fingers. But I would be very careful with that and not overexercise. Alternatively, hand grips follow the same principle, but try to find some that offer as little resistance as possible. And please run this suggestion through a specialist if you intend to attempt it, because I am not a qualified physician and can only recommend what I have learnt from people who are actually qualified.