An out-of-stock product disappears from the catalogue. That does not automatically mean its direct address was removed or that search engines cannot index it. Stock status, catalogue display and technical reachability are separate states.
Compare the direct product page with shop and category listings. Record whether the item is temporarily unavailable or permanently retired. A useful retained product page may still make sense when restocking is expected.
Inspect the appropriate settings
WooCommerce provides inventory settings controlling out-of-stock visibility. Products also have their own publishing and visibility settings. Variable products can involve stock at the individual variation level.
A fictional record separates the questions:
Product published? yes
Direct product page reachable? yes
Stock available? no
Visible in catalogue? no
Reason for exclusion? inventory setting to inspect
Check whether backorders are allowed. This can influence which options remain purchasable. Do not change it merely to improve appearance: it affects what customers can actually order.
After a deliberate change, test an available item, an out-of-stock item and a variable product option. Compare product pages, listings and the basket. Availability should remain understandable throughout. If the product page should also leave search results, inspect its indexing directives separately.