They've already said they won't make panic moves if they whiff on Kawhi. I doubt they'll continue to pursue Horford without a commitment from Kawhi.
If this offseason doesn't pan out, it's not the end of the world. Shai, Shamet, Zubac and Harrell can still improve, Kabangele will get a chance to develop, and we can still build through the draft - including with the coveted 2021 Miami pick. It won't be a quick fix like landing Kawhi would be, but I trust the front office to draft well.