Will my bar codes ever expire?

No. Once your bar codes are issued to you they are yours for life. There are no future fees. 

You would assign a given UPC/EAN (GTIN) to a specific product and it would stay with that product for life. When you cease manufacturing/selling that item you would not reassign that GTIN to any other product. The assigned GTIN would stay with the product itself, for life. While it is possible to reuse a GTIN, it is not recommended and many stores do not allow you to reuse them.