It has been taken as alpāyumr̥tyu in the commentaries. 

On Fri, Mar 24, 2017 at 2:00 AM, Martin Gansten via INDOLOGY <indology@list.indology.info> wrote:

I wonder if list members might throw any light on the term alpamṛtyu occurring in a 17th-century Sanskrit text (Yādava's Tājikayogasudhānidhi). I would have supposed it to be a scribal error for apamṛtyu (in the sense of 'untimely death') were it not that the metre requires that the first syllable be long. I do not recall seeing the word in other Sanskrit texts, but a quick web search returns quite a number of hits in the vernaculars, including some from the Rāmcaritmānas. However, I am not sure from these whether to understand alpamṛtyu as untimely death (= akālamṛtyu), as a nearly but not quite fatal accident, either, or as something else entirely.

Martin Gansten