The phrasing is old fashioned, probably because you are reading a translation that was made in the ninteenth or early twentieth century. A modern writer of American English would likely write the two words or else instead of the one word else. Otherwise would be a good substitute, but again or otherwise would likely be more common.
One of the defects of the English lexicon is that there is no universally accepted way to distinguish between what mathematicians call the inclusive or and the exclusive or. The phrase A or B means A alone or B alone or both A and B: or alone is lexically inclusive (although logic may indicate that the meaning is exclusive). It is equivalent to the Latin vel. Latin had the form aut A aut B to mark the exclusive or: A or B but not both.
A else B is one old fashioned way to form an exclusive or. I prefer either A or else B, but the only way to be sure that every English speaker will grasp that you mean an exclusive or is to exclude the possibility of both A and B explicitly. The usage of else in your example to mean an exclusive or unfortunately did not catch on.