10 years is a longgg time. WoW might not even last 10 more years, and Honor Buddy definitely might not last 10 more years. Who knows. No one. HB + Blizz are currently in a lawsuit mess. It is supposed to continue in 2016.
Considering I purchased my key in 01 2012, I would say 7 years left after 3 amazing years is definetly a possibility. If nothing else, the features and price alone is worth it.
81 years? Interesting number. Would like to know why 81 years. Are you going to die at 81 or in 81 years or wow will last another 81 years or Hb will last 81 years from when you bought it or another 81 years from now? Questions...questions. But NamedNoob already answered, as long as the HB part of Bosslands Empire is in business your lifetime licence for HB is good.