The CW has
cast Maisie Richardson-Sellers as the new/old Vixen on Legends of Tomorrow. Her character, Amaya Jiwe, won't completely replace Mari McCabe. Mari will still appear on the Vixen series and possibly Arrow/Flash. Here's the character description from the CW
Amaya Jiwe – better known as Vixen – is the newest superhero to board the Waverider and join the ranks of the Legends of Tomorrow. Like
her granddaughter, Mari McCabe, Amaya’s powers are derived from the
mysterious Tantu Totem, which allows her to magically access the
abilities of animals.