I'm curious what could happen to my teeth if i brush them but them have a salty snack before bed?

Salty snack?: The salt in the snack is of little concern but what is comprising the snack item is important. Leaving food materials in your mouth for several hours can allow them to be broken down by enzymes and bacteria. This will result in attack on your teeth and inflammation of your gums. This can lead to cavities and periodontal disease. Bad idea.

Eat, floss, brush!.: As others have said, it is not the salt that is of concern. It is the "stillness" of the oral environment that allows the breakdown of foods into sugars which remain undisturbed ; forming plaque while you sleep. Eat your food, rinse your mouth out with water, floss, then carefully use a toothbrush in vibratory motion at your gum-tooth interface. (no sweeping or stroking) then sleep better!