The phrase welp he's dead works as a shorthand reaction online because it states the obvious in the most casual way possible. Clips like this spread through gaming, meme edits and short form video where a sudden death needs a punchline that is faster than an explanation. Instead of shock or mourning, the line treats the loss as final and slightly expected, which is why creators reuse it for knockout moments, ragdoll falls, failed stunts and characters who are defeated before they can react.