Menu links point at live store content, so deleting content affects the menus that link to it.
Before you delete
When a resource's delete confirmation reports menu impact, it shows for each menu how many items will be removed and how many will become labels to keep their child items — so you know the navigation impact before you confirm.
Automatic cleanup
Shortly after the delete, menu items that link to the deleted content are updated automatically. An item without child items is removed. An item with child items becomes a label, so its dropdown and every other link in it stay in place. Your store's activity log records what changed and why.
Until that update finishes, storefronts already leave out links to deleted content, so shoppers never follow a dead link.