Wow, sorry to hear that.
Don't really know if I can help you with any tips or something, but it reminded me of a smaller accident I had maybe 5-7 years back involving mainly my left thumb. For the few months (3-6), I had a real trouble pushing the thumb against my index/ring finger. I couldn't use my left hand anymore for squeezing the shampoo bottle, for instance. It just hurt too much. (I'm lefthanded, play righthanded). After the first few months, it kept coming back and disappear for at least a couple of years...
Anyway, I cannot recall having any major difficulties playing the bass/guitar at that time... Maybe it was because I've always kept the action quite low. Perhaps you could try a super-low action. It doesn't work on all basses but it would reduce the force you need to push the strings to almost zero. You could also try to support your index with the ring finger when you want to press it down.
I had another injury in the gym in August last year. For 6 months, I couldn't lift anything straight upwards with my left arm when laying down (benchpress) or when sitting up (which was even harder). I got the advice not to stop using the muscles that hurt but start using other machines involving the same muscles. When I did that, it gradually went better. It hurt in the beginning but now I'm back where I used to be... Just told you this story too because what seems impossible now might become better if you start over with a slightly different approach.
Hope you don't have to switch to a lefty... I definitely wouldn't like to do that unless it was my only way out.