If you are being looked at strongly for a job, and the headhunter that is trying to get you in drops the ball, if that is your question, then the answer is clear to some extent.
By this time the company should be known to you, if not then you are SOL, but if you do know the name of the company, you can do three things.
Spend time and talk to the agency that is representing you, find out what happened to the rep that was representing you. If the rep doesn't get back to you in an adequate amount of time (a few hours, give or take time for lunch) then call back and ask if someone else can represent you.
If they are unwilling or know nothing about you or the job in question, then ask them to take your name out of contention and go to step two.
Call another agency up, and say that you were looked at for a job, but the agency that was representing you is no longer because they dropped the ball, and would like to have them represent you. Say what your financial compensation was, and go from there.
If they are any form of agency they will take a lead and run with it, especially with a candidate that was already vetted and was almost ready to be proposed to in the first place.
If they don't want to go to step three.
Snail Mail the company, send two certified letters, one to the HR, and another to the department you were attempting to get the job at. Explain your situation, and say that you are willing to talk to them directly as long as their policy allows such a thing. For some companies will not talk to people directly unless they are through an authorized representative company.
If you can't or don't want to do these things the best of luck to you, I've gotten jobs through this way before, I know it works. It may seem odd, but sometimes perseverance will get you a job...