I have noticed that wikis are listed as being subscribed to items even after the sitelinks have been removed and the wiki is not making any other use of the item.
Example: https://www.wikidata.org/w/index.php?title=Q22941194&action=info (which will probably get deleted soon) lists svwiki and cebwiki as subscribers, even though both sitelinks were removed. The svwiki page was edited to be about another item and then the sitelink was removed from Wikidata. I turned the cebwiki page into a redirect and then remove the sitelink from Wikidata.
Another example: For https://www.wikidata.org/w/index.php?title=Q22950526&action=info, I also edited the cebwiki page to turn it into a redirect and then removed the sitelink from Wikidata and it still lists cebwiki as being subscribed.
It seems that in other situations, the subscriptions are being removed:
- https://www.wikidata.org/w/index.php?title=Q27728384&action=info does not list svwiki. The svwiki page was deleted which caused the sitelink to be removed.
- https://www.wikidata.org/w/index.php?title=Q27221100&action=info does not list svwiki either. The sitelink was deleted from Wikidata and then the page on svwiki was moved.