Is it obligatory for the seeker of knowledge to shorten the duration of his studies to return to his parents for fear that some harm may befall them before he can teach them, or is his remaining for study better? And is it permissible to inform them that their religious state is the cause of his sorrow, even if that leads to their sadness, with the intention of making them feel the danger and his fear for them of Allah’s wrath?

Go and study, and do not be troubled by whispers [from Satan]. You can communicate with your parents through social media. Do not despair because of their lack of uprightness, for "every soul, for what it has earned, is pledged" [Qur'an 74:38], and your duty is only to advise them with gentleness and kindness. Do not tell them what would grieve them, but rather lead them to uprightness gradually. As long as your parents are monotheists, they are on goodness, and you should advise them kindly and pray for them.