Slavery won't stop just because it's banned.
Neither will trafficking.
it will be greatly reduced. the ban just isn't imperial law anymore which didn't apply to morrowind, it's an edict from king helseth, and with the alliance of hlaalu and dren, the main source of slaves will dry up. also not many are that willing to cross helseth and his men.
sure there'll still be slaves around, and ways to get slaves, but it's no longer an open market, and the sload aren't going to bother with it, and just get bodies other easier ways.
i'd thought the telvanni would be interested with the sload, but they aren't.