It's not clear to me how important porn is to reddit; it's possible reddit could ban porn without upsetting most of their users. Not every site with porn is doomed.

In the long run though, I expect reddit to ban porn. It might be a few more years, there are a lot of factors in play, including the patience of their investors and whether or not an influential media company decides to do an exposé on reddit hosting amateur pornography without vetting peoples' ages and/or hosting professional pornography in violation of copyright law.