The longevity of purple ombre hair depends on several factors, such as the quality of the dye used, the individual's hair type and condition, and how often they wash and style their hair. On average, semi-permanent hair dye can last 4-12 weeks, while permanent dye can last until the hair grows out or is re-dyed. It is best to consult with a hairstylist to determine how long the purple ombré will last on your hair specifically.