I haven´t read this whole stuff, but i guess, in your case, you would have to take this imaginary landscape and transform it in a way, that it does not require your bought tool anymore (make it a completely independent standalone landscape/product), like baking all the textures etc.
Otherwise you would just have created a dataset for this tool, with which the tool, and any user who bought this tool, can recreate your landscape… something like a preset or a mod. In such a case, i would assume, in best case scenario, you could only sell this data without that paid tool, AND with a big fat warning, that it absolutely requires tool XYZ from another user to work (which probably would be the dealbreaker and prevent your dataset from being released as a standalone product).
However, you could try to partner with that other creator, and see, if he likes your dataset enough to include it in his tool and give you a fair share from his sales.