Take a similar piece of material that is larger than the hole by a good margin. Place it on the INSIDE of the bag and stitch it in place. And don’t be shy with the stitching: let your adventures shine. I’ve done this on a number of bags that have made unaided descents and it works out fine. If you want you can darn across the borders too (darning just means running stitches over and over it).

If you only need the cuffs tight when it’s raining or otherwise adverse, just throw a couple of elastic hair ties in the pocket. When the need arises, put them on the outside of your jacket right at the top of the cuff (“up” from your hand). It’ll hold tight and perform just like a tight cuff. Bonus points: throw in an extra one in case you are with someone with long hair and you can pull one out and offer it up when the unexpected hits. I do it for my wife and she appreciates :)