It seems Apple Maps will pre-download route data when a route is planned. If an internet connection is unavailable then there will be less detail available and searching will not be possible. But the pre-planned route will be there.I'm familiar with Apple Maps in that if I ask Siri for routing directions to a direct point "B", my iPhone uses Apple Maps in the background. I'm also aware that at least inRoute uses Apple Maps for the presentation layer of their iPhone app. Right now, I have concerns about that architecture. Apple map data (which inRoute uses) is stored in temporary iPhone cache, which by definition isn't permanent and is not guaranteed be loaded. There are offline navigation scenarios where you're basically screwed until a data connection can be restored. I understand these situations are probably rare, but if I'm riding through unfamiliar badlands out West, I'm not taking navigation availability risks. So no Bueno.
But I digress. I'll download the Apple Maps app from the App Store and play with it.
If frequently operating without a data connection then Google Maps offers the ability to download and store map data. Not sure about complex routes with GOOG though.