F1 Visa Stamping

[hellosrpm]

My son entered USA on H4 visa and now he's doing PhD now under F1 visa. After visa transfer from h4 to f1 he never crossed the border. I am thinking about the possibilities for him to get his visa stamped in Canada. If just in case the stamping gets rejected, can he re-enter USA back based on automatic revalidation.

We have an emergency and he has to go to India. Any advice would be appreciated?