No chronicle, inscription or hagiography records an actual death for Gorakhnath. The scholarship that debates his period treats it as a span of activity rather than as separated birth and death years, and Nath tradition itself holds he attained a deathless, perfected state through hatha yoga rather than dying an ordinary death, so no source within the tradition he founded proposes a death date either.
What would resolve this A dated inscription, monastic record or textual notice external to Nath hagiography naming an end to Gorakhnath's activity or a named successor's own dated era.
OpenHistory of Hinduism, Nath Sampradaya studiesDavid Gordon White, The Alchemical Body: Siddha Traditions in Medieval India