If a category is moved:

example - "Photography" category moved :
old location: "All categories > Other collections> Photography"
new location: "All categories > Photography".

The favourite you had set on "All categories > Other collections > Photography" becomes obsolete and redirects to a page with all the items of the website.

If a category is deleted :

example - "Plants, Seeds and Bulbs" category deleted :
before deletion: "All categories > Other collections > Plants, Seeds & Bulbs"
items transferred to: "All categories > Other themes & collections > Unclassified".

The items in this category are transferred to a replacement category.
The favourite you had set on the deleted category "Plants, Seeds and Bulbs" becomes obsolete and redirects to a page with all the items of the website.

 

In either case, we invite you to delete your old favourite list and create a new one.

More information in these articles:

Add or delete an email alert for a favourite