Hi,
In your last message, it seems that you're talking about the backend display of the products.
It's normal that you don't see the products in the products listing anymore since you removed the products from all the categories.
The products listing of the backend uses the category of the products to know which products to display on the listing. Even if you go in the Root category (the main parent one) and set the filter to display "all sub elements", the system will only display all the products attached to at least one of the product categories under the Root. And in your case, you removed the category of these products so they are not attached to a category anymore and thus won't display there anymore.
If you want to access them, you can edit another product and in the URL, change the id from the id of the product you're editing to one of the ids of the products without any category and you'll see that product.