in Iran-India relationships India is to lose more. In bilateral trade between the both countries India is importing 80% - 90% of the total trade of around 14 billion dollars in 2009/10. In another words if India stopped bilateral trades with Iran, there will be many products that will be effected resulting in inflation. Also there are chances that Iran will get one step closer to Pakistan and India wouldn't want to see that.
I don't think India will do this mistake, they will continue maintaining strong relationships with Iran and will not agree to any kind of sanctions
India HAS to abide by the security council resolutions. There is no choice.