So do I, @DominicX, But I rarely conjugate verbs with -st and -th. So I was suggesting that they do not necessarily belong in the same era, “whence” is not archaic and does not mandate an archaic verb because it is still in use in modern times. By separating them you do help bring them back.
I would also argue that idiomatically you don’t really need a verb, not as long as you can also say things like “Whither the Republican Party?” But of course you do if the aim is a complete sentence.