It will come back. Hairloss, after all, isn't your hair falling out; it's the follicles failing to regenerate as strongly, so that in each successive growth cycle the hair will be shorter, thinner, and more lightly colored until it doesn't grow back any more. A non-male pattern baldness sufferer typically loses up to several hundred hairs per day; the Finasteride is merely synchronizing this loss (as I understand it), but these hairs will regrow -- and if Finasteride is effective for you, they'll grow back in better shape than they were before.
The timeline above is enormously helpful. My early days on Finasteride conformed to it exactly. However, as a word of warning, the shedding is different for many people. I shed in month two and three, then again (much more) at month six, and a little bit at month nine. I didn't think it was working. But it was. Just search this site's discussion archives and read the dozens and dozens of stories by people who are anxious about shedding. It happens. It sucks. It can be disspiriting. But if you really want to know if finasteride works for you, you'll need to perservere until about the twelve month mark. (Due to all the up-and-down of shedding, I wasn't certain it was working until quite late in the first year of treatment.)