Check your analytics every 3–6 months. If a piece that used to perform well shows declining traffic or views, it's time for a refresh. Don't wait until it's completely dead.
Yes — refreshed content often outperforms the original because it combines existing authority with updated relevance. YouTube and Google reward updated, current content.
Only delete if it's harming your channel (misleading, low quality, off-brand). Otherwise, redirect or refresh. Deleted content loses any existing links or traffic it has.