Despite the usual Slashdot non-believers it's a dead certainty.
As soon as Google bought Motorola Mobility, it was on the cards that Samsung would look elsewhere. The fact the Google could potentially favor their own hardware development team, rather than a licensee, is strategically enough to change Samsung's strategy.
The other big issue is the App store. I see figures bandied around of anything from 80% to 94.7% of Android ecosystem revenue going to Samsung devices. If it's anything like that, Samsung will have their eyes on the 30% developer fees they can take from their own App store, rather than that going to Google.
Also, with the Tizen's Android compatibility layer built right in, it's effectively telegraphing the market that Samsung will switch to Tizen. Just a matter of time. I think sooner, rather than later.