Permanent Monster Familiars

Since they're permanent, they'll just heal when not in use right? o_o So technically you could have 1 forever, but having a 3 vitality familiar would make it definitely indefinite?

(sorry, never used one before. All I knew before was that if you didn't get new cards every time, they would die).

the orbs above their head is their "energy" if you like. Everytime they attack they use some of this energy. Once they use up all of their energy they disappear(not permanently, just go into hiding like a hungry pet). Once they go into hiding from running out of energy there's a cooldown, as CarrionCrow said, before you can summon them again.