[Plugin: Simple Taxonomies] Taxonomy terms don’t go away when post trashed

I’m using Yoast Simple Taxonomies for workshops at
https://juliadean.com

On the home page, at the bottom left, I’ve got a list of instructors which is built from the Taxonomy “Instructors”.

But after a workshop is over, we delete the post. The related instructor stays in the list, though the only post they’re related to has been deleted.

When you click on one of those instructors (Pilar Law for example) you get a 404 Error.

So my questions:
a. Is this how it SHOULD work (not a bug but a feature) ?
b. Any way to stop it ( IF taxonomy has posts, show tax, ELSE do not show )?

Right now, I’m just using Yoast Widgets for that. I know barely enough to substitute some PHP for the widget.

Thanks,
Jim