AS per recommendations all coronary artery fistulae except very tiny ones should be closed. because there is tendency to grow with time and associated risk of endocarditis, heart failure, angina, etc. if you are not closing them you should follow them closely and keep a watch on change in size or any complication.
Yep - close them if you can. We do see adults with originally "small" fistulas - but they grow over time and then you have young adults with atrial fibrillation at the age of 30 or 40 - bad quality of life