Nothing will happen . You will only miss your chances to get into nits iits and a few other centrally aided colleges.
There are tons of other examinations for you to write

Nothing will happen but u will not be eligible to get any nit,iit this year if u have chances left prepare for jee main and advanced this year by taking a drop

Nothing actually. You will miss your seat at nits or your chances for iit. That's not everything , you can go and crack other top entrances. If you are so desperate for a seat at a national institution better drop a year and reappear next year. 

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