We're getting users that think their tickets are being deleted since there's no notification when their post gets merged.
Ah good point, I can see how this is a bit jarring.
I'm thinking the notification would be something like "Your post, Notify users for merges, has been merged into another post" with a link to the new post where they'll see the merge in the activity section?
Or maybe it'd be better to just trigger an instant notification email. Just thinking aloud, gonna have to think about the right experience here.
On a slightly related note, when you merge a post (e.g. A merged into B), the URL for Post A no longer works (does not redirect or indicate it was merged), but just has an error message. This is really hard for a user (with no notifications as well) to follow along with and check for updates.
@Lenny Beckerman-Rodau: Received a similar report recently, agreed that this should be smoother.
Update: URLs for merged post now redirect to merged-into post.