Since tires have gotten so big over the years and few people carry a spare anymore, repairing a cut sidewall may become a reality. I have personally seen many sidewall punctures getting repaired on the trail, using both patches and the stitch/plug methods.
Here is a good video of the patch method: https://www.youtube.com/watch?v=fgvgYZOfNcM
Some stictching: https://www.youtube.com/watch?v=_bctAjk0MCI
