I'd like to know if it's correct to take the expression out of as a single structure with its own meaning or it's just the union of the prepositions out and of. I'll give a couple of examples:

A creature out of this world.
He is out of danger.
My uncle is out of town.
His head is out of proportion with his body.
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OED says about out of;

out of prepositional phrase

"Out of" is originally and still in writing, two words, namely the adverb "out" followed by the preposition "of" (in its primary sense = from). In analysis "out of" is precisely on the same level with the obsolete "down of", "up of", and the current "forth of", "out from", "out to", "down from", and other instances of an adverb followed by a preposition which defines its relation to an object. But in Old English as in Old Saxon and the Scandinavian languages "út of" ("út af" in Old Swedish, Old Norse, "ut af" in modern Swedish, and "ud af" in modern Danish) became the regular equivalent of Latin "ex", Greek "??" or "??" (while German and Dutch used the adverb itself as a preposition); "out of" has thus acquired a unity of sense and also of pronunciation, which entitle it to separate treatment from "out" or "of", whereby also its own sense-development can be more distinctly exhibited.

The history of "out of" is partly parallel to that of "in to", with the differences that the latter is now written "into" as one word, and that "out of" is the opposite, not only of "into", but also of the static "in". One reason why "out of" has not needed to be written as one word may be that the distinction now made between "into" and "in to" is in the case of "out" expressed by "out of" and "out from": thus "They came me", "They came my house", "He went me", and "He went my house".

In each case, I believe 'out' to be an adverb followed by a prepositional phrase.

There is another possibility, but I will leave that for those who know more.
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Any other point of view?
 paco2004's reply was promoted to an answer.