enigma1 - 1:54 pm on Aug 9, 2011 (gmt 0)
Which of course means duplicate content for these URLs:
If you set it up right you shouldn't have the duplicated issues. I think you posted the principles already so basically if
goes out of stock you drop the navigation and all dependencies generating links to that page.
Requests made to the old page may return a 200 with the new content you want to display (of a similar item). It shouldn't show (for long) as duplicate content because the link will is no longer generated from within your domain, so google should clear it up.
That's one way of doing it. Another is with 301 which is more effective but you lose ranking of the old page real quick.
Also depends how often the catalog is updated. If you update often (eg: 2nd hand items, in/out of stock different products) is not a good idea to let the out of stock pages flooding the SEs index.