Will a surgery for a funnel chest ever revert years after the surgery is done?

Yes. Pectus excavatum can recur after surgical repair. This is particularly true when the repair is done before puberty. For this reason, most repairs are now done around 14 years of age. The overall recurrence rate is somewhere between 1-3% and is higher in patients with underlying connective tissue diseases.
No. Once the surgery is done "funnel chest" does not return.It is a congenital deformity and contrary to many peoples' idea that it "compresses the heart and lungs"this is not true.
No. It would be unlikely for funnel chest to recur years after a good repair. The bones do remodel continuously throughout life. However once the ribs growth pattern is modified by surgical repair and ribs are calcified they remain stable in configuration.