I don't see why Scenario #2 necessarily results in Hillary losing. For that to happen, either Trump or McMullin would have to win in the House, and I'm not sure that's so certain.
Trump himself is very unpopular among some people, and among some members of Congress as well. If push came to shove, I'm not sure we could count on a party-line vote by the GOP to choose Trump over Hillary. There might be enough defections that Hillary would actually win.
If that is possible, then for Scenario #2 to be a sure thing, we'd have to count on all those Republicans voting for McMullin. And I'm not so sure of that either. Sure, a lot of Republicans would prefer him to Hillary. But I also think a number of them would be extremely uncomfortable with the idea that some guy who is virtually unknown by 90% of the country, only really ran in one state, and only won in one state dominated by a single religious minority, should be chosen as President. Some of the RINO's might believe that is sticking a finger in the eye of all the voters in the other 49 states. In fact, I personally believe that McMullin winning a fight in the House is the least likely alternative should it make it that far.
I'm not saying that is definitely what would happen. But at the same time, I don't think there's any guarantee that forcing the House to choose between Hillary, Trump, and McMullin is an easy "Hillary loses" scenario.