I am still playing on WotLK and planning to update, but i don't wanna lose my characters so i am leveling until i get heirlooms so i could level easier after expansions, but i was wondering. Do you lose heirlooms when you get a new expansion? If you lose them then i can just update my game instead of wasting my time getting heirlooms.
You can't transfer your characters to other expansions. If you want to play on MoP, you will have to make a new character. You also can't transfer heirlooms to other expansions. So you won't be able to use your wotlk heirlooms on MoP realm.