I don't think anything will take its place. Lucario plays a lot differently. And if you try to use it like you try to use terrak, you're going to struggle. Mienshao is more of a momentum grabber, hard hitter and pressure mon rather than terraks rolls. I believe the teams that use terrak will just use another adapt hard hitter or a strong as fuck rocks setter like garchomp, I don't think fighting type was the main reason aside from good offensive STAB why it was used the way it was used.