Hi,
Both redirects & leaving as 404 (or 410) are valid options.
If you are removing this entire category & corresponding products because you stop selling them - you could put a custom 404 (or 410), explaining the visitor that the products are no longer available and you could indicate the alternative products you can offer them.
According to Google (https://support.google.com/webmasters/answer/2409439?hl=en)
"When you remove a page from your site, think about whether that content is moving somewhere else, or whether you no longer plan to have that type of content on your site.
- When moving content to a new URL, redirect the old URL to the new URL—that way when users come to the old URL looking for that content, they’ll be automatically redirected to something relevant to what they were looking for.
- _When you permanently remove content without intending to replace it with newer, related content, let the old URL return a 404 or 410. Currently Google treats 410s (Gone) the same as 404s (Not found). _
Returning a code other than 404 or 410 for a non-existent page (or redirecting users to another page, such as the homepage, instead of returning a 404) can be problematic. Such pages are called soft 404s, and can be confusing to both users and search engines."
You also might want to check this article http://searchengineland.com/googles-matt-cutts-seo-advice-unavailable-e-commerce-products-186882
If you still sell the products - but you moved them to another category, or if you don't sell these products anymore, but you offer very similar products, you could consider putting a 301 to the alternative categories/products. As example you stop selling white tulips "Amsterdam" - but you still have white tulips "Utrecht" - you could redirect the first to the second. They are not identical, but an acceptable alternative for most visitors.
In your specific case - I guess that you removed the category, but that it will be coming back next year. In that case, it's maybe better to keep the pages, but only remove the links to these pages. On the products themselves, you mention something like 'pre-ordering start in Jan. 2017. Check out of fall offers" and you mark them als "out-of-stock". You then just remove the links on your site to this subcategory. (this is quite similar to e-commerce shops with specific Christmas pages - these remain online all year long, but are online made visible as of September)
The reason why Webmaster tools is sending you the message that these pages are not found is just to inform you. It could well be that these 404 are unintentional, and by informing you you can take the necessary measures. If the 404 is intentional, you don't really have to do anything.
Just make sure that you also update your internal linking - to be sure that no internal links go to the pages you removed. Screaming Frog can help you to check this.
Hope this clarifies,
Dirk