Yes yes, you can still get organic traffic.
First of I want to clear your doubt. Sitemap is not a ranking factor. It is SEO techniques which help you to crawl your site smoothly and so on your content get indexed in Google.
Google just crawl links everywhere, and sitemap is one of them. So sitemap just help you to index your site content on Google. Wikipedia does not have any sitemap, but their internal link structure is good, and hence their site is crawl often.
If you want to know how Google crawl website, then checkout this old white paper.