I have survivors guilt almost every day. Why have so many of my friends died while I'm still here? Of course, if I had died, neither of my two beautiful daughters would be here either... something they have told me more than once.
Early on, I remember feeling absolutely suicidal, but that has passed with the years. In your case, I'm sure the guilt isn't as strong, but your concern and your care for your wife shows your true feelings. She is first and you wish it had been you. Just continue to care for her and do your best to sort out the mess left by someone who shouldn't be allowed to drive anymore. No matter what happens, as long as you and your wife have each other, nothing else matters.
In a few years, you both will look back on this, hug each other, and remark, "You know, it could have been so much worse." Give yourself time to get to that point.
I'm not religious, so I can't pray for you, but I can hope that everything turns out for the best for both of you. I had a new car for three months when I got rear-ended much like you were. Unfortunately, in my case, they didn't total the car, the 'repaired' it. It never felt the same ever again and I ended up trading it in at a huge loss a few months later on for another car. Now I look back and realize that killing the other driver probably would have been a mistake, no matter how much I wanted to. Now I realize that continuing to live well and being happy that his insurance dropped his policy is the best revenge.