In a case like this where the product is built and available, how is a cofounder supposed to work? Part of being a co-founder is taking on the enormous risk and not-being-paid (yet at least) for the early work. If most or all of that work is already done (especially if you already have paid customers), what does a cofounder bring to the table in exchange for taking a massive chunk of the equity you've built up? Do you just find a co-founder who is an investor and can at least bring some money to the table? But, then why would you care about YC?