i'm not too sure they're really "dead" per se, in many lores they were once humans who resorted to unspeakable acts like the aforementioned cannibalism, and thus possesed by the wendigo spirit. some lore suggests a silver stake/bullet/blade to the heart, others suggest fire since they are winter spirits and thus have a weakness to heat, but the main point seems to be to destroy the heart.

a wendigo, or windigo depending on your spelling preference, is a malevolent spirit in native algonquin culture. they feed on human flesh and are born out of selfishness and greed, or from committing taboo acts like resorting to cannibalism out of starvation. once you're stalked by a wendigo, they're near impossible to get rid of. it's either kill it or get killed. or, as per some legends, be nice to it and feed it real food and it might turn back into a human. no guarantees tho.

my guy, i believe you encountered a wendigo. godspeed soldier. fire will kill it, but only if it's engulfed. git yourself a nice flamethrower