Don't know who the culprit may be, but you will certainly have new buds. Impatiens continue to produce buds throughout the growing season.
......Jan

I finally figured out the culpert--- it is a rabbit I caught him in the act. I've started using a repellant and miracle grow and hopefully things are starting to turn around as I am seeing new buds forming. I also had to cut some of the old stems back as they were so badly damaged.