All counter values have an upper limit before they will overflow back to zero.
In modern devices this is probably a 64 bit integer (unsigned), giving a maximum of 18,446,744,073,709,551,616 bytes or packets before a counter will overflow.
Probably nothing to worry about in this lifetime. Upgrades and various outages will reset such a counter before it ever reaches that figure.
If you do happen to cause a 64 bit counter to overflow - damn boy slow down! Save some Internet for the rest of us. :-D