Falling in line is about supporting the democratic process, win or lose. No, one isn't obligated to fall in line, but if you're part of a political party and you believe supporting that party and its ideas, you really shouldn't have problem supporting your parties nominee even if that person wasn't you prefered candidate. I'll give you a pass if you're an outsider but if you're someone who has registered part of a particular party for years on years and then throw a hissey fit when your prefered nominee doesn't win then I stop to question your grasp of the political process.
If you don't agree with the majority of the party...become an Independent or join another party! Otherwise your end up looking like a child who threatens to take their toys and go home whenever someone doesn't see eye to eye with them.