Magnafluxed, now what the F
When somethings magnatized it has an excess of e-, or electrons. It's like the balloon you rubbed on your head as a kid and stuck on the wall. It will demagnatize naturally. Everything in life wants to be balanced. Those extra electrons will find their home by grounding out somewhere, and it will happen quickly. You're fine.
Not in this case. That's static electricity which creates an electro-magnetic force.
All iron (and thus steel) has magnetism. The 'net' magnetic force is a result of alignment of the electron spin (nothing to do with extra electrons though). That spin direction can be influenced by outside forces, which is what the magnetizer did to his block. Typically there's enough randomness that there's no net magnetic force, despite still being magnetic in nature. Each grain of the metal will typically have it's own spin alignment, and at the macro level that randomness results in a net zero force.
Unless the magnetizer magnetized the majority of the block (unlikely), then the magnetic field will slowly decay on its own as the spin of the electrons in the magnetized area will be influenced by the non-aligned spin of electrons in the non-magnetized area. Heat the block up, and it will go faster. No need to take it to the 'curie' temperature either. Anything which excites the electrons will help speed up their re-alignment. Normal heat cycling, time, etc will all eventually decay the magnetism.
Demagging the block would be important if machine work is to take place immediately after magna-flux. But if you can wait a week or two, or even bake the block as part of the cleaning process, then it's not likely to be much of a concern. Attempts to remove the magnetism may cause more problems than they solve, or just be wasted effort in the long run. In a production shop, or small parts (which area easier to completely magnetize in the first place), de-mag is far more crucial.
Since OP is already seeing a reduction in the magnetic force it is not likely that it will be long before it becomes a non-issue. By the time the machine shop gets to it he should be fine.
