It's a building, not a monument. Knock it the rest of the way down, put up a marker if you want and put the land back into use. Make it an open space park or something. There is nothing special about a former industrial site.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now