I don't think the Republican party has been sleepwalking for the last few months. They simply have been unable to stop Trump, because, after all, people have been voting for him. Perhaps if there hadn't been such a divided field from the start Trump would have only had to fight against one or two candidates. But there was, so he had the advantage for that, and has milked it for all that it was worth and then some.
I don't think that many people are going to mourn the withdrawal of Ted Cruz from the race. Anyone who bothered to pay attention to what Trump and Cruz were saying will have seen that Cruz was right-wing in the sort of way that makes Nigel Farage look like a communist; whereas, ironically, one of Trump's problems with the Republican party is that he isn't actually right-wing enough for them.
So, Clinton v. Trump it is then.