What will happen to me if I don't have surgery for a chiari malformation?

Hydrocephalus. Fluid will build up in the ventricular system of the brain with a resultant increase in pressure inside the brain/skull.
It depends. The finding of a chiari i malformation may or may not be associated with symptoms. If there are no symptoms and no neurologic dysfunction, surgery is not necessary. What happens over time varies. Most adults with an incidental finding will not eventually require surgery but a few will. One should be made aware of noteworthy signs and symptoms.
No change. I suspect you refer to chiari i found incidentally on mri. This is probably just a incidental finding and may not be clinically relevant. However, consider it has been there all of your life and that you have lived with it 22 years. Unlikely it will change in the next 22 years.