This question already has an answer here:
How do you do SEO for sold out products? Please share your approaches:
- for products, which are unavailable for a limited time frame (seasonally)
- for completely sold out products, which will be never more become available in your shop
I'll edit the question, because i realized, it isn't fully clear for all, how many different question are related to it:
- noindex soldout products or not?
- redirect them to homepage / category page / sitemap?
- what redirect to use: 301 or 302?
- do nothing, beside of a notice for users?
- fire an error? which error? 404 or 410?
- what to do with incoming external links?
ps: i mean this question is not a duplicate to the mentioned one: the mentioned question origins from the year 2011, where SEOs were talking about pagerank and meaning it would be important. Now we have completely different paradigms. Beside of this, the mentioned topic has no answers to some questions i'm interesting in.