Questions regarding National Conventions and the American electoral process.

In 2010. Republican Senator Lisa Murkowski of Alaska lost the primary to a TP candidate. She then ran a write-in campaign in the general election and actually won. She is still a loyal Republican.

On the Democratic side, the 2000 candidate for Vice President was Connecticut Senator Joe Lieberman. When he ran for reelection to the Senate in 2006, he was defeated in the Democratic primary. But he ran in the general election as a candidate of the “Connecticut for Lieberman” party. He won. In 2008, he went on to give a speech at the Republican National Convention endorsing John McCain for president. He continued to serve in the Senate as an “independent Democrat” until he retired in 2013.

Note that a number of states have “sore loser” laws. Generally, these laws prohibit anyone who ran in a primary and lost from running in the general election. It is not clear whether a state can apply its sore loser laws to presidential elections.

No, the losers don’t compete in the general election, not with their party’s label anyway. They could run as independents, but that’s much harder and they are very unlikely to win, which is why they run for the nomination in the first place.

Delegates are on the ballot for particular candidates (or behind the ballot, perhaps.) If the local leaders back the establishment candidate, say, and the insurgent wins, they won’t be going to the convention. Thus superdelegates, who are assured a seat.
When I was in college a friend of mine, more or less as a class project, ran as a McGovern delegate, won, and went to the 1972 convention. His parents were active in local Democratic politics so it was not totally random, but he certainly had no major qualifications besides being above voting age.