A slaughtering of Trump maybe gets the party back on course. That said there is still a chance the far right conservatives demand one of their own in 2020.
When Trump loses, three things will happen on different corners of the Right:
1) Establishment conservatives will write him off as a fluke and continue with business as usual
2) His supporters will claim he was stabbed in the back, especially if the RNC effectively renounces him and Republican officials continue to disavow him or at least tamper down their support. This will lead to them becoming even more bitter and angry, likely leading him to being the early frontrunner for 2020
3) The Tea Party/Religious Right/Radio Right will, as always, claim that he lost because he wasn't conservative enough, leading them to push for an even more hard right conservative. Ted Cruz is already positioning himself for his 2020 campaign.
