Ambrose Beirce, the Battle of Tierra Blanca and The Devil's Dictionary

Ambrose Beirce was a remarkable wit under any account, but the ambiguity of his fate cast a long shadow on history. If we take the most common account, by no means certain, then he was last seen headed in the direction of the Battle of Tierra Blanca, where, if we take Carlos Fuentes conjuring of what might have been, he was an imaginary witness to the actual Ivor Thord-Gray's lucky shot, as he was trying to make the most Pancho Villa's only pair of 77mm canons, as portrayed in the movie "Old Gringo"

People criticize fictional historical accounts the most when they tread a little too close to the truth. Nobody minds a good yarn so long as it doesn’t take itself too seriously, which is not a problem for this film, where Pancho Villa and Emiliano Zapata are fused rather effectively into a single antagonist, while our Beirce-like protagonist casts a weary light on the ambiguity of idealism:

Politics, n. Strife of interests masquerading as a contest of principles. -- The Unabridged Devil's Dictionary

What really happened to Ambrose Bierce?