This is getting into the "great unknown" kind of territory... but here's my take:
Henry is in the dog house after the Raiders game. He started off the season well, but the legal issues and injury have really impacted his performance. He's still the best back on the roster for hammering away at the enemy defense, hence why he got the call in the 4th quarter against the Chiefs.
Young is quicker, more explosive. He can break off big runs and do some damage on screens / flat routes. However, the biggest knock against him is the inability to stay healthy. He was the starter against the Chiefs, and given his performance I suspect the starting job is his to lose at this point. Really, he's a very nice fit for an offense that seems to be developing a knack for hitting big plays.
Majority reps for Young? It certainly looks that way right now... but remember "majority" is just one more than the other guys. Andre Hall has also shown some flashes this year, so I wouldn't count on any of our backs getting more than 15 carries a game (barring injury). To be honest, that may be the best thing for Selvin Young's career. The downside (from the FF perspective) is that if another back is used to get the "tough yards" that will tend to mean that other back also gets more of the red zone touches.
Given Henry's problems this year and contract, I doubt Denver either trades or cuts him. I think the split/committee at RB will continue into next year.