It is absolutely unacceptable for a Muslim to sit where alcohol is served. But if the Muslim sat and that happened, then it is imperative for him before anything, to inform people around him about the evil of drinking alcohol or sharing the table with people who are consuming alcohol. If such happens, it is incumbent on him to seek God’s Forgiveness and repent, and increase in His obedience. Allah, the most high, says: Indeed, good deeds make misdeeds go away. That is a reminder for those who remember [Quran 11 : 114 ]. And one must not return to something like that ever again.