How to Repair a Crochet Blanket

It sounds like you are using a knot to join the yarn together. Instead, use a darning needle to thread the unused wool into the work on the wrong side.

This depends on the kind of stitching used. If you have a basic stitch like only single crochets, double crochets, etc., you unravel until you reach the end of the last partly intact row and crochet from there as if this side is the bottom of your project. Nobody will notice if the last few rows are upside-down. You could even do this for a simpler stitch out of the category of textured stitches like the moss stitch. For anything more complicated, whether it can be done depends on the type of stitching. You could unravel further until the last intact row and tie off there as if this was the intention, but that depends on what kind of project you have (a sweater would end up too short).

If the squares have separated where they were sewn together, you'll have to find some matching yarn and sew them again. Be sure to leave a "tail" that can be woven back into the squares for added security against coming undone.