So based on this, I assume that all access to your calendar server (iCloud, Exchange, Google Apps, etc) was managed through a centralised server(s) that Sunrise used... for something.
Maybe the next time someone claims to be a funky new take on just do a little checking. We've had desktop and mobile device clients for mail, calendaring, contacts etc for literally decades. Why now, when we have more computing power available to us than ever before, do we need another server (operated by a company that's more likely to disappear than not) between us and our mail/calendar/contacts?