If I were to do Botox treatment would it cause my chubby cheeks to sag or jowl? (Photos)

From the photos, it doesn't seem that you have a very wide jaw with thick massester muscle, however, its possible to further narrow your width, but an in person evaluation would be necessary.

Without an in-person examination, or thorough discussion of your symptoms it is difficult to offer advice on masseter hypertrophy. I would seek out an in-person consultation with a local board certified plastic surgeon.

For starters, you are supposed to feel the master muscle when you clenching your teeth. From the photographs you have provided it does not appear that you have excessive mass that are muscles. And it does not appear that you should undergo a Botox treatment. I can only recommend that you have an in-person consultation with a plastic surgeon like myself to determine what it is that you would like to achieve and whether or not a treatment is indicated. I hope this helps and good luck from New York City plastic surgery