The magnetic flux of a magnet can be lost due to exposure to high temperatures, physical damage, or being placed near other strong magnetic fields.
Yes, it is possible to restore a magnet's magnetic flux through a process called "re-magnetization".
To re-magnetize a magnet, you can either use a strong external magnetic field or expose the magnet to high temperatures and then cool it down slowly.
The time it takes to restore a magnet's magnetic flux depends on the size and strength of the magnet, as well as the method used for re-magnetization. It can take anywhere from a few seconds to several hours.
In most cases, a magnet's strength can be fully restored after re-magnetization. However, it may never be as strong as it was originally.