TL;DR: Migrations should be one-way and do nothing but move the question to the most appropriate site. That site can then handle bad or off-topic questions as though freshly asked.
At present, question migrations that go sour and are rejected get locked on their destination site and unlocked on the source, which has two results:
- They are ignored on the original site, because no one notices them being unlocked (since, as I've verified, they aren't bumped)
- They are worthless on the new site, whatever the reason for their being closed — and that includes closing as "Unclear"
What this doesn't do is Provide direct feedback for rejected migrations.
This lock shuffling is therefore, as far as I can tell, a misfeature, something no one really asked for, no one actually wants, and that does nothing but get in the way of anyone doing anything useful with the question. So when a question is closed on the target site, go ahead and increment the counter of rejected migrations for 10k stats, but don't do anything else. (Migration is currently designed to avoid cross-posted questions getting a confusing mix of answers by locking all but one copy of the question. This is fine, but rejection should not unlock the question on the original site as it does now. Instead, the original copy should just stay in locked-stub purgatory until it is mercifully Roomba'd.) Sites can already handle closed bad questions, even those that are truly off-topic in every way; they don't need any extra locking to make things more complicated.
This is especially fun, as alluded to earlier, when a question is specifically closed because it needs to be edited by the author in order to be answered (Unclear, various custom close reasons currently put under Off-Topic, sometimes Too Broad or even Primarily Opinion-Based). A more pointless, dispiriting waste of people's time cannot be seen on Stack Exchange. Someone has to notice that the question got locked (it won't be bumped), and ♦ flag it. Then a ♦ mod has to unlock it. By this time the asker has probably noticed something is strange, dug around, and perhaps tried editing the original asked on the wrong site, which will merely uselessly send the post through the Reopen queue without any actual chance of being reopened. If they ever do get around to editing on the right site, it's probably been days, and the confusion and bad feeling from being given such a thorough runaround is difficult to overestimate.
Is there anything I've missed that gives rejections any faint vestige of value?