They will be deleted when the post is deleted otherwise they will stay in the Media Library (which is a good move). I tested this on a couple posts to make sure they would delete. There are redundant images only because that image is imported every time the post is imported, which is going to happen unless there is some other mechanism to do it, but right now I say leave it. There will be a max of 40, which is a lot, but that can be changed in the feed settings and there are only 25ish posts right now.

I am closing this to-do. Unless there is something else.