Wow that sounds like a horrible fall, and very scary. As most of us find out the hard way, head injuries bleed profusely which exacerbates the alarm.
So two things: Sidewalk - where I live that's the county's responsibility. I have to keep them clean, because they are in my property line, but repairs and uneven pavement are the county's job. Not the homeowner. Different jurisdictions might have other rules, city, county, state, etc.
Your wife does walk with a bit of a low scuff - she's fallen before. I do that, some shoes worse than others. I'm more prone to tripping and catching my foot on something than other people. I'm the one who gets static shocked all the time because of it. I'd probably face plant if I didn't see a 1" raise in a sidewalk.
My advice would be put this all out of your mind for the next 30 days. Don't bring up suing with your wife, if she does, refocus the discussion on her getting better. Deal with all of that, and once she's healed up then see how you feel.
Then if you're still inclined, talk to a local injury lawyer. You likely have at least 6 months or longer to file if you decide to go that route. I think this just gets chalked up to an unfortunate accident, vs. provable negligence, but I'm no lawyer.