aa-globe

This plugin has no settings. 
Just activate the plugin and check if sold out items have moved to the bottom of the list.

Catalog Sorting by Stock Status – In Stock First, Sold Out Last

This plugin changes the sorting of a catalog (or product category) so that out-of-stock items are always at the end of the list

Risto Niinemets

Most commonly taxonomy sorting plugins will create a new interface to drag or order/sort your terms. This plugin uses the built-in view just to make things easier. Just grab the term and drag it to a new position. No more extra clicks – everything is saved after repositioning!

The Taxonomy Sort

I would advise against using this plugin. In the latest WordPress update, selected categories are no longer displayed on the posts page. Deactivating the plugin shows the selected categories once again. It's too bad, this was a useful tool.

Broken in WordPress 4.7

Allows you to easily change the order of different taxonomies/terms/categories.

Catalog Sorting by Stock Status – In Stock First, Sold Out Last vs The Taxonomy Sort