The link from that question isn't to a specific chat room, and still goes exactly where it is supposed to go (for me, at least).
Read the description again.
The link points to the custom "chat room not found" page, because that is the page that has the image the OP is asking about.
In general, the best way to handle dead links is to find an appropriate replacement URL, and fix the link without changing content.
Failing that, removing the link and putting a notice that the link no longer works is appropriate. However, in those cases, you should include a text version of the original link, as the context of the URL might potentially be helpful (either in providing information about what the citation was, or clues for those looking to fix it).
Just make sure the link really is broken, first.