Will Also Bought display out-of-stock products?

Also Bought only displays products that can be purchased in your store.

You can control whether an out-of-stock product can be purchased or not with the following option in your product editing form, inside your Shopify admin:If you have disabled the selling of out-of-stock products, they will be automatically removed from the Also Bought recommendations. Once the product is restocked, it will appear again as a recommendation.