Yes, but you'll at least have the API definition. And you work at the same company, so you can show up at the desks of the team responsible and demand answers. And if it breaks in production you get to page them and they have to wake up and help you! The threat of pages is a great way to coerce decent documentation. It's an important principle at Amazon that if a production service has a dependency on you, then you are also a production service. Another benefit of breaking things up into SOA is monitoring individual services. If your API is returning 500s then it's your fault and your problem (at least until you can root cause to one of your own dependencies that's returning 500s, then you can pass the buck).
