Jonah:
The phrase “or else” is much older than your previous correspondent suggested. The phrase definitely existed in Middle English. Chaucer, who died at the end of the 14th century, used it often, most famously in his “Complaint to His Purse,” which you can check out [here]
In the poem–a satiric love-ode to his empty purse and intended to make the new king laugh and send him some cash–Chaucer implores his money-sack, “Beth hevy agen, or elles moot I dye!” (“Be heavy again, or else I might die!”–delightfully pronounced, in Middle English, “or ellis motey dey-uh!”)
The word “else” (“elles”) is even older, from Old English, and crops up in _Beowulf_ and other Anglo-Saxon poems and prose works from the 10th century or earlier. I couldn’t find any *specific* examples in the small corpus of surviving Old English texts to suggest that it was used to mean “or else,” but it may have been, because even back them it had most of the other current meanings and usages (such as “otherwise”).
Such questions are fine pasttimes for drowsy medievalists on cold, snowswept Fridays.
UPDATE: He sent me this follow-up email:
Cancel that last email! Just re-read and saw you were looking exclusively for “trailing” or-elses. My apologies–please ignore previous e-mail!