The establishment republicans don’t really want Trump as their nominee. They would support a third party candidate such as Romney and a vice president running mate, who has the possibility of delivering a large amount of electoral votes that would not allow any of the canidates to achieve a majority and that would be Ohio governor John Kasich.
The election of the president will be decided by members of congress who will vote along party lines with Paul Ryan, a republican and former running mate of Romney in the 2012 Presidential election. Ryan will be directing them how and who to vote for. And as Kurt Vonnegut would say, “and so it goes”.