Deciding to drop out from IIM Calcutta is definitely a very difficult decision. One has to go through a lot to make it. Now if you get a repeat year don’t get demotivated. The first step should be to analyze the reason for your failure.
In case of sickness or personal reasons: Such reasons should be given a second chance. Don’t just give up your bright future just because you failed to accomplish it in due time.
Failed in certain subjects: There are two scenarios to be considered here. First, you are confident that you will now put in extra effort and make it through. Then you should definitely repeat. But if you are not confident and think you won’t be able to make it again then don’t waste your time and efforts repeating. It’s normal not to be able to accomplish certain things that others can. There are always other options that might be better for you.
The most important thing is what your reason for repeating the year is. And honestly, you know best whether you should repeat the year or not.