May we all know what this startup's product is? If your co-founder really believes in the product then do something that one of the co-founders of RethinkDB did

May we all know what this startup's product is? If your co-founder really believes in the product then do something that one of the co-founders of RethinkDB did, keep working on the product as a side-project. Nothing stops you both from working on it as a side-project, even open sourcing it could give it a new life and open up new opportunities.