What happens to the posts in a category if I delete the category?

What happens to the posts

I deleted a category that had exactly one post in it, so there would be no doubt about which post the deletion touched. The post survived. Its own address kept working exactly as before, and it stayed on the blog's post list. What changed was its Categories field. Where it had named the deleted category, the field came back empty. The post is left uncategorised, not hidden and not removed.

What happens to the category's own page

A systeme.io blog category is a page of its own, at an address in the shape /blog/category/<name>. I checked that address from outside the dashboard before deleting the category, and it returned a normal page. Straight after deleting, the same address returned a 404. A second category, left untouched, was checked at the same moment and kept returning its normal page, so this was the deleted category's own page breaking, not a fault on the blog generally.

The warning mentions neither one

Deleting a category opens a small popup titled "Confirm action", asking "You are about to remove this category. Continue?" with Cancel and Confirm as the only buttons. It does not say how many posts are in the category, and does not say its own page will stop working. The list you delete from already shows a post count for each category, in a column of its own, so that number is known and left out of the warning anyway.

What I have not checked

I did not test whether creating a new category at the same address brings the old page back, or whether the deleted category still shows up anywhere in the blog's own menu or filters. I also did not look for a redirect setting for the address once it starts returning a 404. None of this is answered here.