<p>If we want to take a firmer line:—</p>
<p>Moderators can close the cross-site duplicate using a custom reason (neater than using an inappropriate default close reason). If we think there's value in keeping it here purely to link to the duplicate on another site, we can up-vote it, which will protect it from automatic deletion. In fact any user can vote, up or down, so an advantage of this approach is that the decision isn't made by a single person.</p>
