So I just got a post I made merged with another topic, and that's fine. However, it would also be nice to be notified of such actions, since it isn't always that easy to find where it was moved - thank you.
You can always look in your Profile under comments to find the new location. There's even a search function.
(The software probably doesn't have the feature to notify you, just as with removed or locked threads - https://en-forum.guildwars2.com/discussion/comment/303745/#Comment_303745)