I hate to break it to you, but I’m pretty sure the only way unblurring would be possible is if you have the original unblurred source video. Blurred areas simply contain too little data to reconstruct the original. The artifacts of the unblurred face are not stored in the resulting video file for literally every video file type in existence today.

Even using AI to unblurr a video, you would need to show it at least one unblurred picture of the face to properly reconstruct the same face in the original video. Otherwise the AI would just guess and put a random face in place of the original. The regeneration technique you are describing is still science fiction and only exists in movies and television shows.

Edit: your edit is still incorrect. There is no such video editing tool called “unblur.” You can sharpen an image, but there is no way to undo a blur unless you still have the data from the original, which a final exported video does not. The act of blurring removes information, and you cannot rebuild a photo from information that no longer exists. Blacking out faces is in no way necessary for the reasons that you are suggesting.