Does it ever happen that someone posts bail and does not go to court to stand trial?

Yes. This actually happens quite frequently. When someone is in jail and wishes to get out while awaiting a trial, the judge may grant the person bail. The judge might also let the person go on his own recognizance. When the judge lets the person go on his own recognizance, there is a higher chance that the person will actually not show up for his or her trial than when the judge grants a bail for the person to get out of jail.

There are two ways in which a person may be apprehended after he skips trial. If the person has funded the bail on his own, then the law enforcement agencies in the area, state, or country will track the individual down to try to bring him back to court. The defendant then becomes a fugitive of the law.

If a bail bonding agency put up money to get the defendant out of jail, then the bail bonding agency has a vested interest in getting that individual back in front of a judge. As such, the bail bonding agency will employ bounty hunters to track down the defendant and return him or her to jail. The bail bonding agency may also escort an individual to court on the day of his or her trial just to make sure that he or she shows up. The U.S. is the only country that still allows legal bounty hunters.

In some cases, the defendant merely missed his trial date. In other cases, the defendant is on the run. A great deal of either private or public funds will go into ensuring that the defendant is tracked down and returned to court. 
Remember, when someone pays a bail bond, the money will be turned over to the court if the defendant fails to show up to court. As such, a bail bonding agency or a private lender stands to lose thousands of dollars if a defendant skips court. For this reason, a great deal of resources are generally put into ensuring that an individual makes his court date.