If it is thrown to the House, Trump wins
The only chance of the election going to the House would be if the race is super tight, and Johnson wins Utah. He has no chance in other states.
I think it is dangerous to assume that if the election was thrown to the House that they wouldn't pick Trump. You might wish that sanity would prevail and they'd pick an actual adult like Paul Ryan, but that's very unlikely IMHO.
Here's how the process would work when the republican majority House members met behind closed doors to determine their strategy:
1) Some actually support Trump and would signal their intention to their colleagues that they are voting for him no matter what
2) Some would believe it is wrong (or feel it is bad politics that could cost them their next re-election bid) to choose someone that didn't even run for President, or perhaps ran but wasn't nominated, and would signal their intention that they feel forced to vote for Trump
3) A few might think that way but dislike Trump so much that they'd signal they would vote for Hillary over Trump (especially if they were lame ducks and didn't have to worry about political repercussions - at least two retiring house republicans have already announced their support for Hillary over Trump)
4) Due to worries that splitting the votes between Trump and Ryan would send Hillary to the White House, the plan to choose someone other than their nominee would be discarded and enough republicans would get behind Trump that he wins