Even though Credence developed Obscurus because he was forced to repress his magic, he was able to still go through his adulthood. The main reason why he was able to do this is he is a strong wizard. He is alive in the second movie because there was a cutscene wherein he was able to survive and he fled the scene riding a boat.
People thought of the first movie that he was totally destroyed but it seems that his power was able to save him once again. He may be troubled and mysterious but his new adventures are truly worth following.