Pursuant to this discussion - when a TimedText page is attached to a filepage that has content but not a file itself, it still displays the MediaWiki:Timedmedia-subtitle-no-video message. If it's instead a redirect to an actual file, then it doesn't display any warning at all. I didn't check what it says when it's a redirect to a non-file.

There should probably be a different message when the filepage exists but has no actual file, and also a message when it's a redirect to a file as sometimes that means the TimedText needs to be moved to a new name.

(Tentatively subscribing two people mentioned in the village pump thread)