Often times when questions are closed as duplicate, they are simply stated as such and no other information is given. Why is there no procedure for linking to the question that has been duplicated when closing based on duplication. Often times the other question uses different nomenclature to ask the same question that may not be known to the person asking. I understand that the person asking should search first, however if they do not recognize the alternate wording of the other question then they will not see it as a viable answer, and simply marking the new question as duplicate without linking to the old helps no one to actually get the answer they are looking for.
The link is given above the question:
As far as I know, it is not even possible to close as duplicate without giving a link to a question on the site (which is sometimes troublesome, e.g. if duplicates are on other SE sites, Wikipedia or another canonical source).
The only way I can imagine that the link vanishes is if the linked to question is deleted. If you find examples of that, please let us know!