I think 95% of gamers will continue to game on Windows with or without Xbox games. I also think that some gamers will skip buying an Xbox if the Xbox doesn't have any exclusives.
Maybe MS doesn't believe that or care. Maybe they will start placing all Xbox games on Windows 10. I think they will continue to have Xbox exclusives. I don't know. Time will tell. I do know they will do whatever makes them the most money.
I think console gamers will continue to be console gamers... If Xbox 'exclusives' were suddenly all on PC, I don't think people who prefer playing on consoles are suddenly going to get a Gaming PC to play those games... They'd prefer to get a windows10 console. As they like the efficiencies that come with having a wide adoption of a standard hardware...