If the plea agreement that you are writing about concerning your friend was entered in open court before a judge, the deputy district attorney, your friend and the presumed attorney of your friend where there was a court reporter present taking down what was said, the oral plea agreement in court would be binding regardless of the fact that not all parties have signed the written agreement memorializing the oral agreement.I suggest that if your friend has a criminal defense attorney representing him or her that he or she press the district attorney's office to get the plea agreement signed.