I know that Emmett has said that he'd return to Hollyoaks if KR ever left the show, so that Stendan could have a happy ending. This makes me kind of hope that KR will eventually want to move on from the show, but not sure that I see that happening any time soon.
I definitely see McHay making a strong effort to make their relationship work, so they might last a while - but no, I don't see them together in the long run. Ste's too self-centered, and I don't see that changing any time soon. Then again, his character evolved a lot after he had his first two kids (for instance, the person that he is now would never leave someone to possibly die in a car wreck like he did to Amy when he was younger, or threaten to jump off a building just to make someone pay attention to him), so maybe a new child will give him an extra push to mature and become more considerate.
I also think (and here's me defending Ste again) that he's been through more than the average character on the show, so his self-centeredness is derived from his survival instinct; he's constantly having to look out for himself at the expense of others' feelings, because he has so many hurdles to get over and is in a constant mindset of expecting everything to turn out horribly.
Can't wait to see how it works out either way!