Your co-founder's code is mostly worthless at this point without the continuing involvement of the co-founder. Developers have their own idiosyncratic coding styles, and without a multi-member dev team providing continuity of design, I expect that a new developer would rewrite it as the product evolves.

At the same time ... if you've been at this for 6 months already and you don't have any meaningful traction, you should strongly re-evaluate whether this is going to be a viable market for you.