Yes, you just need a piece of matching morph to fit into the "hole," designated as demolished. I suppose you could SEO existing and revised morphs to get that piece.
However, I should say that Meshes work FAR better for terrains, because you can cut holes in them much easier, as well as gravitate level dimensions and landscaping. (Gravity doesn't work for morphs.) I'd recommend you replace the terrain morph with a mesh.
Richard
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Richard Morrison, Architect-Interior Designer
AC26 (since AC6.0), Win10