Waterproof mascara, and any mascara, won't make your lashes not grow back in if they fall out. However, if the lashes are ripped out, then over time the lashes can stop growing in. This happens with tweezing as well, resulting in bald patches. And I do believe that this can happen with body hair if using an epilator or waxing for a number of years, the hair growing in thinner and with less of it. So as long as you are cautious with makeup removal, then you shouldn't worry about it. If you notice that your lashes feel and look thinner, then it could be that the mascara is irritating the skin/follicles and thus causing some issues, but it wouldn't be the fact that it's waterpoof specifically causing that issue. I had that problem with a Clinique mascara because the ingredients just did not at all agree with my lashes, they felt like they were in much poorer condition. Much like when you wear your hair up or use hold products, having mascara on all day will make it seem like there are more lashes falling out compared to not wearing mascara for a while since there is no way for the lashes to easily fall away from your face.