Does the servant's persistence in certain sins, and the resulting fear and concealment from people, lead him to shirk and nullify his deeds?

Perseverance in sin is to persist in it and not desist from it. There is no necessary connection between it and Shirk (polytheism), nor does it affect the acceptance of good deeds unless the Sacred Law explicitly states so. For the one who persists in sin to conceal his sin is less severe than for him to commit it openly. However, perseverance in sin is a grave danger that may lead to Kufr (disbelief). Concealing oneself from people while brazenly committing sin against Allah is blameworthy, as Allah Almighty says: "They conceal themselves from men, but they do not conceal themselves from Allah." This may lead to the nullification of good deeds or the dominance of hypocrisy.