<p>A <a href="http://meta.stackexchange.com/questions/35744/allow-diamond-moderators-to-reverse-question-migrations/126982#126982">question that is migrated to another site is rejected</a> by that site if:</p>

<ul>
<li>it gets deleted</li>
<li>it's closed as Not Constructive, NARQ, Too Localized, or generic Off-Topic</li>
</ul>

<p>To reject a question that's been migrated here, you should vote to close for one of the reasons listed above.</p>

<p>When a question is rejected:</p>

<ul>
<li>it's unlocked (but not reopened) on the source site</li>
<li>any answers that were deleted as part of the migration are undeleted on the source site</li>
<li>all migrated answers are deleted on the destination site</li>
<li>the migrated question and any answers received on the destination site are locked on the destination site</li>
</ul>

<p>I can't find a definitive reference, but there are a few mentions of rejected migrations being deleted on the site they had been migrated to.  (After 30 days?)</p>