The reason I mention it is that tree died at around the age of 200, more or less; no one knows exactly when it was planted. It was already a large enough tree that it served as a good spot to commission the American army. Supposedly, during the revolution, the American army was commissioned by George Washington under that already large and majestic tree, which was probably a little under a century old at the time. For that historic reason, there was a desire to preserve it until such time as it died a natural death. For the last part of its life it was struggling—for a number of decades.
After ill health was shown, it managed to survive another 40 or 50 years, suggesting that that possibility exists for this tree, at least potentially. There may be some other reason. It may be that Dutch elm disease, which did not exist at that time, is a more formidable opponent. I throw that out more as a comment than as a question, to say that there are situations where trees that are not in perfect health can survive a fair number of years.