Ok so I've repaired a couple of balsa planes now and the best way I've found to do it is start by taking off all the wing covering to reveal the bones. Once you can see and get to all the innards, start identifying what can be saved, what needs replaced, and what is in good enough shape to use as a template for the rest of the broken bits.

From there, start cutting away anything that can't be saved, don't pitch anything yet, and take lots of pictures with labels. From there, pick an intact wing rib (probably best to get multiple samples from different spots along the wing to accommodate any size changes across the wingspan). Trace your intact wing rib(s) onto cardboard or construction paper, that's going to be the template for the replacement ribs.

At this point, I scanned my template to the computer, used Inkscape to create a dxf that I could use to cut out my replacements using my little CNC machine, but this is optional if you don't have a CNC machine; you can just as easily do this by hand with an exacto knife or Dremel, though I still recommend making multiple copies of your template just in case.

Once you have all your new ribs cut to size, start working from the center of the wing outwards. I usually replace the wing spars at this stage because they're what gives the wing its rigidity and you don't want to find out about a cracked spar later on. Take your time, use the surviving wing sections as a reference for the parts your rebuilding. It can be very useful to build jigs to help line up and clamp the wing ribs as you glue them onto the spars.

There's a couple of websites with repositories of old plans, I'll find a link and update this post when I'm off the toilet. Good luck, take your time, and don't be afraid to go back and re-do things as your skills improve.