I think that after so many votes, delegates are freed up, IIRC.
“Pull out” is a relative term; they still “belong” to the candidate if the candidate was properly on the ballot. (Some states differ.)
THIS IS WHY WE STILL VOTE FOR FRED.
Draft him.
Interesting question.
bottom line answer: Irrespective of state rules and others such as the older Rule F(3)(c), which officially bound delegates to the candidate they had been elected for on the first ballot, the delegates are always free to vote any way that they wish.
Delegates are normally chosen for their long standing involvement and commitment to that party and are presumably not likely to go rogue or in the parlance, “faithless.”
The campaigns put the delegate slates together are not going to put anybody but the most committed loyalists on the ballot.
I know of no way to reverse any vote by any delegate.
What happens to the delegates? Up to them.
I look for nothing new in a brokered convention. - The nominee will be one at, or right at, the very top.