By far the likeliest scenario for the outcome of the GOP delegate race is that Trump gets a plurality but not a majority. Right now I’d put the odds as being about 70% Trump plurality, 25% Trump majority, 5% everything else, including bad accidents, which let’s face it are far from unknown in situations in which extremely powerful political institutions see genuine disaster looming.
A lot of what’s left of the Republican party is trying to game out what to do on the basis of the assumption that Trump gets a plurality that’s not merely formal (in other words what happens if he’s a significant number of delegates short, so that flipping a couple or three dozen doesn’t get him over the line).
By this point I’m guessing that a lot of these people are in triage mode, and are assuming that, absent some unforeseen developments, the 2016 presidential race is pretty much a lost cause, and the goal should be to avoid too much down ballot carnage. As Scott points out, either a Trump or Cruz candidacy is likely to be disastrous for the GOP in terms of winning the presidency, and perhaps in terms of other races.
Thus the fact that the only even vaguely democratic alternative to nominating a plurality-winning Trump is Cruz complicates things. Cruz, like Trump, is an almost-certain loser in the general, so why go through the trouble of denying Trump the nomination to pick a horrible candidate that everybody in the establishment hates with a white-hot passion? The answer I suppose is that there’s a good argument a Cruz candidacy would do less down ballot damage, and especially less long-term damage with Hispanic voters. But is that enough of an incentive to arm-wrestle the nomination away from Trump? I doubt it.
The third alternative is to pick somebody who basically didn’t win any votes, either because nobody voted for him or her, or because the white knight wasn’t a candidate at all. I just can’t see this happening. Yeah back in the 19th century some candidates who had a plurality of delegates going into the convention didn’t win the nomination, which ended up going to somebody coming out of right field. That’s about as relevant as as arguing that Zach Greinke should throw 60 complete games this season because Old Hoss Radbourn did it back in the day. A choice that ends up simply ignoring the entire primary process would probably do more down ballot damage than choosing either Trump or Cruz.
A fourth alternative is to let Trump get the nomination and then run an alternative third-party candidate. I think this is a little more likely than a white knight, but not much. It takes a lot of organizational energy to even put something like this together, and I question whether that will be available after the powers that were have finished slamming Jack Daniels and Xanex while watching Patton on repeat loop. (BTW what are the odds that Trump is consciously or unconsciously modeling his schtick on George C. Scott’s speech to the troops? Scott even looks like Mussolini).
TL;DR: It’s going to be Trump, and it’s going to be a full-on disaster for the GOP.