Referential integrity?

Does this module maintain referential integrity between the gallery node and the referencing images? In other words what happens if you delete a gallery node? Are the images within the gallery deleted as well?

no. there was no such goal to make that.
my client may have situations with one image in two galleries(add by url possibility in the bottom of "edit gallery form").
But for usual cases there you can add free not placed yet in any gallery images to the gallery.

May be there is a need in bulk deletion of "free" images, page with this nonreferenced free images - but for now we do not need that.

also if you want - you may help to the project. as a trick - there is use node reference field to organize gallery so you it's easy make simple module to delete gallery even with it's images. so I close this support request, because for now we do not need such integrity.

Of course you may write addon module for this feature or get another sponsor of a project to get it ;)