Question

Does the pole strength of a magnet decrease with time?

Answer 1

not if it is isolated from other magnetic fields.

Answer 2

If you magnetise something with a magnetic field, its dipoles line up, so normally support each other. But give it a big enough 'push', and they will become disaligned to the point that they do not self-support. You can achieve this by heating it up.

Answer 3

But essentially, your question is not specific enough, as it is totally dependent on circumstances.