I have a friend of mine who is going through the same situation.. Well friend, the answer depends on what you’d want.. Its a dream for an engineering student to study at an IIT.. but some branches at some NIT’s are too at par and even better than IIT’s .. I personally believe that it’s the mind set that will count on ..wether you’ll flourish or turn waste.. If u have confidence that u can do well next year then go ahead..drop a year.. but i do have news that may seem important to you..jee will include one more exam(completely subjective) right afte the JEE Adv for selection into IIT’s from 2017.. so if u are confident on succeeding the very next year then go ahead.. otherwise u can join good NIT’s with your rank(if its general rank)..
All the best (do tlak seriously with your family in this regard cuz it may change u’r life)