As someone who sews....
quite a bit I have been called upon to repair and resurrect some strange things.
What you have to do is stabilize the area underneath the rip with a good supporting fabric. Flannel backed satin would be a good choice, moleskin (not really from moles) would be great if you can find any. Use a 4 to 6 mm stitch on the sewing machine and a thin bead of Aeleen's tacky glue over the lines of stitching to prevent it from pulling through the vinyl bag. Then you can install the snaps without the bag pulling apart again. It is possible to install a zipper in place of the snaps, but then it is no longer original.