You could delete the product, and you could even do 301 redirect for SEO purposes, but up till now, there was no good way to keep the product while marking it permanently out of stock..
The concept is from WooCommerce Ideas Forum.
The option is in the stock status drop-down, and it works for either simple products and variable products...
Upload the plugin files to the wp-content plugins plugin-name directory, or install the plugin through WordPress plugins screen directly..
Activate the plugin through 'Plugins screen WordPress.
Discontinued from the stock status drop-down...
For variable products, can some variations be marked as discontinued and others non-discontinued statuses..
Any number of variations can be marked as discontinued, and it will be reflected on the public facing side of the store...
The following people have contributed to this plugin..
Browse the code, check out SVN repository, or subscribe to the development log by RSS...
Read more