Exactly. It would be too late to mount a viable third party candidacy, but not too late to bring ruin on the GOP. Samson pulling down the temple pillars. Thus I do not think the GOP will go to any such extreme as to bring in a Romney to save the GOP elites and mainstream. All they can do is hold their noses, go eventually with Trump, and watch their party lose. And then offer to rescue the GOP from Trumpistas and Tea Party kooks and Cruz fanatics. I suspect this is sort of what will in fact happen.
"So, for instance, when in a recent national speech, the financial minister of the Royal World Estate of Qualvista actually dared to say that due to one thing and another, and the fact that no one had made any food for awhile and the king seemed to have died, and that most of the population had been on holiday now for over three years, the economy had now arrived at what he called, “One whole juju-flop situation,” everyone was so pleased he felt able to come out and say it, that they quite failed to notice that their five-thousand-year-old civilisation had just collapsed overnight. "
The GOP is fast approaching a juju flop sitatuation it seems.