He bade her farewell whilst flowery is still perfectly understandable. ;)
You're right in that it isn't used as often anymore.
Duo doesn't accept "The priest bade us pray", and it probably shouldn't, but for some reason a lot of us English-speakers seem to like old-fashioned language in church, and it's one of the few places that you'll see bade or bidden still used. (See also "my cup runneth over", "thine is the glory", "forgive us our trespasses" and so on). Maybe it's the influence of the King James Bible being the dominant translation for a long time after language had shifted elsewhere.
Evidence that "bade us pray" is still in use, but probably shouldn't be accepted here, is that it returns hundreds of thousands of results about religious topics, but Google also says "Did you mean Bidet spray?".
Excellent summary! I was just reviewing this sentence and I agree completely.
Much later edit: There are so many who get this sentence wrong for using "bade" that I have now come to accept it. There's no point in enforcing something that gives people unnecessarily.
Hey here's that 'for' thing again.
In "vill du att jag ska mäta dig" I answered "do you want for me to measure you", and it was not accepted, but after I asked about it, my answer was added to the correct answers.
Here I answered again: "The priest asked for us to pray", and it was not accepted, because I added the word 'for'. If it was accepted in the sentence I mentioned earlier, I think it should be accepted here too.