Want to make an adaptation of a fanfic. Do I need the writers permission?

Hey all, there's this fanfiction that I really want to adapt into a comic. Obviously I'm going to make some changes to it so it can fit the comic format and try to put my own ideas of how certain things go.

Would it be scummy of me to make the adaptation (with obvious changes) without the original writer's permission? I tried contacting the writer but they haven't been on the site where they posted the fanfic (seems they've been gone for a long time).

I really want to make this adaptation. But I don't know what to do.