If someone tagged you in a photo or post before you blocked them, and you unblock them later... nothing happens. That tag is dead.
It feels like it should be simple. Just a reversal, right? Wrong. Unblocking someone on Facebook is not simply "undoing" a block. It is a deliberate act of digital resurrection, and understanding what actually happens when you click that button can save you from a world of confusion, awkwardness, and unexpected social dynamics.
No, Facebook will not send them a notification saying "John Doe has unblocked you."