It should not decimate, i think the best choice there is to basically redo the model using simple shapes (so you’ll be able to reproject from view without a problem), as there are lots of faces that are serving no purpose in that model without mentionning those edges that are marked as faces and all the non manifold things.
By example you should be able to retain the shape with something much simpler (and so easier to repair if there’s a problem)
