It is 5 yrs. I had mine in for 5 yrs 7 mths and still didn't have any periods so I assume there wass life in it. You can also have it for longer than 5 yrs if you are over 40 - you can keep until the menopause. I also think, if I remember correctly, that it might be approved for 7 yrs in some countries.
I would imagine it still works as a coil even if periods returned and the hormones have all gone. But don't rely on that - it is just my opinion!!!