Like any beauty product, your results will last as long as you continue to use the product.
For hair serums, like GRO Hair Serum or GRO+ Advanced Hair Serum, since the growth cycle is longer, you'll see your hair return to its natural state in a few months after discontinuing use.
If you stop using the lash or brow serum, things will return to their natural state in about a month, since that's the length of a growth cycle. The serum works on your existing lashes and brows, and since all hair grows in cycles, once the hairs shed naturally you'll see your results fade.