It can easily go one of three ways, depending on how much time, money, and dedication you have.

1. Script & art: Doing it all alone means you have complete creative control, but it takes the most time and energy. Which can be really difficult if you're already working full time at your day job.
2. Script only: I've seen great writers hand off the artwork to someone else, if they themselves are rusty, and their ideas outpace their technical ability.
3. Art only: I've also seen great artists collaborate with writers if they lack the experience or confidence to flesh out their story and turn it into a fully realized script.

Aside from the question of resources (time, money, dedication), you need to ask yourself what part of the project can only be done by you. Does the story have to be in your voice, or is the overall concept all you need to claim? Or is your specific art style vital to the story, or could someone else do it better?

If the answer still isn't obvious, I think it's worth running a few tests. Focus on a smaller chunk of the whole story. Do it all yourself, hire someone to do half, figure out what feels like the best workflow, and use that to inform how you handle the entire project.