Why are you surprised at this? I'm pretty sure it was written in the patch notes about how the buff would disappear after so long or death. I understand you are peeved that you spent 6500 seals on a weapon that you no longer think is worth it, but this was easily avoidable.
sorry can't find it on the patch notes. You mind pointing me the direction cause I only see this.
[dev1381] Sanction-ready gear can now be obtained in exchange for company seals.
“Sanction" is the name given to a process of gear enhancement which involves the casting of any one of a range of enhancing spells on equipment specially crafted to harbor enchantments. The sanction status can be received at the headquarters of each Grand Company, and for the duration of its effect (three hours Earth time) grants a bonus to the efficacy of certain gear. Such gear can be identified by viewing their help text.