None of that's conclusive. The only thing that'd conclusively state that GeoW is never going to a non-MS platform is if they bought the IP. I'm not even saying it's likely, I'm just saying that GeoW is not a MS franchise and there isn't strictly exclusive. If you want a further example, look at Bioware. Bioware also had a good relationship with MS, developing exclusive games for the 360. Mass Effect 360 was MGS, but ME PC was EA. We have no idea who's publishing ME2 (there's talk that Bioware is contractually obligated to give MS another ME, but it's usually by people who have no reason to know such things) but there's already speculation of multiplatform.
Look, all I'm saying is that 'GeoW has always been with MS, GeoW will always be with MS' is, well, a not really that safe. MS has plenty of reason to keep Epic happy, but we have no idea what's going on in their heads. Or not; if believing that it'd never, ever, ever happen makes you feel safe, go for it. Most likely we're not going to see a huge upset there. But then again, Bungie leaving MGS was also pretty unlikely.
How do you know what their agreements are You don't know whats happened since the first one. ME 2 is going to be published by ms as they had the deal for 2 games unless ea and ms worked something else out.
Now i don't know if Epic will be bought by anyone and as far as we are concerned Mass effect's example is currently not comparable to Gears of war.
As for beliving something well I tend to look at things as logical as pssible. Is gears of war selling extremely well on MS platforms ? Yes . Is ms publishing the games ? Yes. Is MS helping or paying out right for the advertising on the game ? Yes . Can Epic make more money by putting it on the 360 and ps3 ? Don't thinkg so. They would have to A) Go with another publisher B) create a ps3 build of the game C) have to pay for all of the advertisig for the game. . D) compete against MS games that they would now postion against gears of war and of course sony games that would be postioned against gears of war.
We also know that unlike sony , MS has been paying for exclusives and dlc. So examples of percieved sony exclusives are not really valid.
Of course who knows ms could just buy epic . They would gain alot as they would get an exclusie engine that was used heavely this gen and of course some strong ips .