I have a bunch of magnets (one of those game-board thingies) given to me when I was a school-going lad over 20 years ago, and the magnets feel just as strong as it was the day it was given.
As a corollary to this question Do magnets lose their magnetism?, is there a way to determine how long a permanent magnet will remain a magnet?
Addendum:
Would two magnets remain a magnet for a shorter duration if they were glued in close proximity with like poles facing each other?
Best Answer
If a permanent magnet could "decay" at the rate given in Rook's answer above there would be none found in geological strata.
A permanent magnet has a permanent orientation of the magnetic moments in a specific vectorially additive direction depending on small crystal domains. To change, i.e. be demagnetized, the magnetic moments have to be randomized by either an external magnetic field or excess heat/melting or vibrations possibly. If nothing like that happens it should be stable. Little magnets in a box left undisturbed would not change magnetisation unless a random magnetic field was in the area .
Non magnetic iron left undisturbed will acquire a field from the magnetic field of the earth, so some change in the orientation of the field could happen to these little magnets, depending on how they lay with respect to the weak field of the earth.