It is extremely difficult to remove the non-stick coating of a pot or pan completely. However, if you have managed to strip the coating and have then sanded down all deep scratches to form a sheer flat surface, then yes, your cookware is still safe to use. The only problem with sanding down a pan, even if one puts all the effort and expense aside, is that the cooking surface will be full of tiny holes as all non-stick cookware is abrasively blasted to a mottled texture before coating.  Technically inclined DIYers looking to strip down away their non-stick layers completely should consider either sandblasting, dipping in a strong acid or aluminum oxide, or scrubbing it away with an electric wire brush. Regardless of which method is used, a lengthy session in an oven at high heat should follow to burn away any coating that may be left over. Just be sure to do this far from animals and with adequate ventilation in the room.