I'm currently in a similar predicament. I've been developing my webcomic idea for a well over a year now, but I'm seriously considering the novel approach. It's taken me this long to want to follow through on an idea I actually like, but it will surely take me decades to see this story to it's proper conclusion... if I were to keep it as a comic.
I mean, it took me until just the other day to make this stunning realization. I could honestly only ever see this as a webcomic before then. I've dropped other story ideas over the years because I could only see them as animated series or what have you, and translating them into comics or anything else just seemed... wrong? But with this story, at least, having it written simply makes more and more sense the more I think about it. Plus there is the option of the occasional illustration.
Hey, it may take you that long, or longer, to change your mind as well. And there is absolutely nothing wrong with that! Or heck, keep it as a comic! A good story can shine through in any medium (though obviously each one has it's strengths and weaknesses, and you should always take that into consideration, yadda yadda, you know all that
).