There are two steps he needs to take right now. He needs to contact a criminal defense attorney in the area and he needs to start the process of turning himself in and hasten eliminating this warrant from his record. He may be able to place the matter on calendar to request that it the warrant be recalled and then ask the court to modify the previous sentence in order to allow for some extra time to complete the community service. While this is long after the previous completion date, turning yourself in is a good sign for the court. In any event, contact an attorney to further advise him. Good luck.
The best thing to do is hire a lawyer to try to clear up the warrant. Until the warrant is cleared he could be picked up at any time and will have it hanging over his head. Given the age of the case, I can't imagine an extended visit in jail, however, one never knows with any judge. An experienced lawyer in your relatives court may be able to help diffuse the situation with the judge and get the issue resolved in a fairly painless manner. Going in on ones own and theowing yourslef at the mercy of the court is always a risk.