Will hair lost due to alopecia ever grow back?

Depends... ...On the kind of alopecia and how long it has been present. There are many causes, from illnesses to surgical procedures to medications to crash diets to stress. Some types of inherited and scarring alopecias, unfortunately, are irreversible. Once you know the cause you can tailor a treatment plan, if treatment is possible. Your dermatologist can help you with this.