Samsung could fork Android, and Google wouldn't have much choice but to put their apps on it, since that's the only game Google has. On the other hand, not forking Android allows Samsung to take advantage of Google as a free software development service. That's also, obviously, the advantage of Android ovr Tizen for them. And, if there's anything Samsung likes, it's having someone else do the heavy lifting for them.
What Samsung is more likely to do, especially as they continue to crush the Android competition, is use their position as the only Android game in town, and on the strength of their Galaxy brand, to dictate to Google what constitutes "Android". In effect, Google will end up losing control of Android and the OHA, and there's not much they can do about it. The one thing they could do is dump Android and try to replace it with Chrome or something else. Interesting that Andy Rubin just left the Android division.
If Google pulls the Map from Android, the platform will collapse immediately. It can replace it with a new one if they choose to do so.