I highly doubt that they would leave Android completely as they would definitely lose a lot of their userbase. Tizen is very much in early stages and doesn't have much developer support and it's not even certain if current devs will port over their applications to Tizen. From what I've heard, Tizen's apps are written in HTML5, which could potentially lose a lot of devs that are not already familiar to web development (can't say much on this since I haven't tried developing in HTML5 before). The most important is still the amount of apps that Android already has. For Tizen to even compete against Android, they must have a lot of quality apps that can compete with the Android market. This isn't a small task by any means and I haven't seen anything extraordinary from Tizen that could possibly convince me that it is vastly superior to the Android OS.
Sent from the current Heavy Weight Champ GALAXY SIII