I'd say MS are most likely to leave first. For Nintendo it's their entire purpose, for Sony, it's about the only thing making them money right now.
For Microsoft, it's a side project for the company and there is shareholder pressure forming for them to drop XB because it doesn't generate enough profit (remembering their idea of profitable is completely different to what a game centric company in the 90s would have been looking for).
Too much investment is required for what many see as limited returns. I think they'll look more to turn Xbox into a multi format gaming brand and distribution platform rather than linked to a box in your front room.