Answered[ Edited ]
It might last for a few days if you didn't take it off, but it is always best to take off your makeup each night. Bacteria, pollution and dirt get on your skin and lashes and you want to wash all this off at the end of the day. I don't know of any actual research that proves your lashes will suffer if you don't remove your waterproof mascara, but I wouldn't try it. My lashes get more dried out when I use waterproof mascara everyday (I have to use conditioner to keep them supple) so I would think that it would be beneficial to have the mascara off for at least night time to give your lashes a rest.