Scott Walker makes a good point here:
Walker also noted the possibility that the vice presidential nominee won’t be chosen by the party’s presidential candidate, as happens in typical election cycles, because the presidential nominee might not be known before the Republican National Convention in mid-July.
“Frankly I think if you’ve got a contested convention, I don’t know that anyone’s going to get to pick,” Walker said. “The delegates may pick the presidential running mate.”
I expect that the delegates WILL pick the Presidential running mate. Under any scenario, including the ones where I wouldn’t be caring about the answer anyway.
While I think that the only legitimate choice for the presidential candidate is someone who has actually run in the primaries, the vice-presidential candidate doesn’t necessarily face that restriction. Since the job is so amorphous anyone can be picked and that pick would be legitimate.