Ngrams only shows the overall use statistics, and not how "else" is used.

The Wiktionary entry at https://en.wiktionary.org/wiki/else lists three use forms;

  Adjective: When all else fails, read the instructions
  Adverb: How else can it be done?
  Conjunction: Then the Wronskian of f and g must be nonzero,
    else they could not be linearly independent.

The claim is, I believe, that the conjunction form (the third one) does not predate its use in programming.

The "someone else" and "nothing else" examples you listed are the adjective form.

The "or" in "or else" is the conjunction, not the "else".

You should be looking for something like " "Yea , but what am I ? a scholar, or a schoolmaster, else some youth".

Another thing to check would be if earlier uses were only in binary exclusive cases, like "One if by land, else two if by sea", or also with 3 or more terms, like "One if by land, two if by sea, else three if by air."

I don't know how to carry out this sort of search.