Merus's life was spared, but they turned him into a mortal. What happened with his powers in this moment? Did his use of Ultra Instinct and strength disappear when this happened, or are those powers unrelated to his former status as angel?
From Dragon Ball Wiki - Merus,
Upon being revived by the Grand Minister, all of Merus' Angel capacities were removed, including his immortality and divine powers, making him mortal [and now] being known as Merus Ikanoichiyabosshi. While nowhere near as strong as his Angel form, Merus is still extremely powerful and capable of using the Autonomous Ultra Instinct ability, being able to even take on the likes of the Transformed Moro thanks to it.