Does anyone know if and how I can repair this bookshelf?

If the broken piece still matches up, I would start by using some wood glue to tack it in place. Then on the underside you can use a metal brace screwed into both pieces. Maybe also add in a triangular wood piece underneath in the corner for added support.

I agree with Tricia. If bare wood shows when the repair is done use some dark wood polish or even a brown Sharpie for touchup. If too noticeable put a potted plant next to bookshelf.

Tricia is on it! Brace it and use wood glue. Any cracked areas can be filled in with plastic wood, sanded and stained to match.

First let me say you have my sympathy for how scary that had to have been. I would simply use wood glue to reattach the leg. Apply glue to both the bookcase and the leg and set in place. The weight of the bookcase will hold the leg in place as the glue dries. Once the glue has dried you can use furniture markers to camouflage any other damage. Good luck to you!

As Tammy very sorry for your scary incident thank goodness no one was hurt. I think both Tricia and Tammy have good ideas or if it is too damaged with some good tools you could make a replacement leg if possible match the color of the book case glue back on with wood glue and use marker shades if necessary. Hopefully you will not have to replace the leg it appears it can be glued back on. If not exact sand down any overlaps and should be good as new. Good luck glad you guys are ok.

Thank you . Yes it was a scary situation and we are all OK. I am going to try Tricia's idea and everyone's ideas also. Everyone is saying to wood glue it. I will purchase some Gorilla Glue. I think that is the strongest glue.

I would leave it alone. To remind me how lucky and blessed I am. Put a flower pot in front of it. I would worry more about the exposed wires.