This question Are constructions like "That's me out, then" primarily British rather than American? is more about "that's"
This question's answers When a person replies with a sentence starting with "then"/"than", should it be then or than? are very close, but the "then" is almost a conjunction there, not an offhand interjection
Related, the "yes", "right", "no", "ja", and "okay" in
- The one around the corner, yes?
- And we'll meet again on Tuesday, right?
- We don't want to be too hasty, no?
- We've covered this topic before, ja?
- So we will only stay a little while, okay?
do not read like classic question-tags as they do not use a form of "to be". They might confirmatory or leading
This is not in the form of a question, but it feels the same to me
- We'll see you at the party, then
Even when the sentence has a question mark, sometimes it's not really asking (allofunctional implicature); I just want to know what that last word is called and if it should ever be "than"