See previous two posts for details. The histopathology results came in on the cat on which I performed the necropsy. Shockingly, this cat had a metastatic carcinoma of the intestine. A clot was indeed found, however it was intimately associated with this intestinal tumor. The tumor likely acutely bled, leading to the formation of a clot, which led to the ischemic event (lack of oxygen) that resulted in the hemorrhagic necrosis of the intestine (see photo in previous post). The clot had absolutely nothing to do with heart disease as the heart was normal. An incidental finding was chronic pancreatitis. A specific laboratory test for feline pancreatitis, which was done when the cat was alive, came back normal.
We certainly learned something from this case.
Such cases are almost as rare as this (addendum: I switched the photo from zebras to this - way cuter).