Technically they could all lose in the long run if none achieve post-show success, because that's what really matters, isn't it? Winning doesn't really mean much if it leads to nothing.
I can't see Union J being a success at all after the show.
I can't see Chris being a proper success but I can see him doing a Mary Byrne type thing. Covers album for Mother's Day which does well. Original album which probably doesn't. Who knows, though. It's hard to say whether his votes will translate to sales.
Jahmene... eh... he's so dull I really can't envisage him doing great as a star kind of thing, but album-wise he has potential I suppose. And like Chris, there is an audience. He's just so uncharismatic and dull, though.
James Arthur could probably do quite well despite his limited talents. He has the most potential of the four, I'd say. It depends on the material he gets/writes.
It's hard to predict though. We'll see!