If Mimic copies a move, that move is used, and Spite successfully reduces its PP, then Mimic's PP in the party structure will be overwritten with the PP data of the copied move. Since copied moves have 0 PP ups applied to them, this means that if Mimic had any PP ups applied to it, then those will also be cleared.
If Mimic copies a move, that move is used, and Spite successfully reduces its PP, then Mimic's PP in the party structure will be overwritten with the PP data of the copied move. Since copied moves have 0 PP ups applied to them, this means that if Mimic had any PP ups applied to it, then those will also be cleared.