Answer: Rinsing the urine off the roots and repotting in fresh soil probably saved your plant. There's hope - Dracaena fragrans "Massangeana" is propagated by cutting off segments of old canes so that they are 3-4 inches long. These are inserted into moist sand until they have rooted and new growth comes from old leaf scars.
While you can cut off the top and try potting it up (or sitting it in a glass of water) so it can develop roots, you can also cut a long segment of the cane and root as above, as well as leaving several inches of cane on the original plant in the original pot. New stems should appear from the cane stub of your original plant, segments of the cane will root and send up new shoots, and with any luck the top of the plant will root in water. With all these propagation techniques, you should end up with several healthy new plants. Best wishes with your project!
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