The only time that springs will "set" is when they are improperly heat treated or stretched past their elastic limit.
Note that the springs on your car are in a continuous state of compression, and they seldom if ever fail. When they do fail, the usual mode of failure is outright breakage, rather than sagging or taking a "set".
Other things that cause spring failure are overheating, generally in the 700+F region;
Sharp bends, holes ordeep tool marks in flexed areas; Extreme vibration; corrosion, and the like.
The only spring failures that I have seen in my own firearms over the last 30 years are due to breakage. This has never occured in a magazine, bit usually firing pin springs or
Generally speaking, a well made steel spring properly designed for it's intended use should last upwards of 100K cycles.