I have been researching this, and the answer is a bit disappointing. Months, not years, if the wigs for women is worn daily.
Even as little as 3 months! The less wear, the longer a wigs for women will last.
The deterioration is in both the quality of the hair strands (natural or synthetic) and the basic structure of the wig (hair loss). As far as I could find out, the wigs for women cap is less prone to deterioration than the hair part of the wig.
If someone is wearing a good quality, human hair wigs for women, you should not be able to tell. The partings are made to look real, the hairline looks great and they sit well on the head.
However, if someone is wearing a cheap synthetic wigs for women with no parting and a terrible hairline, it’s very obvious.