Yes as according to the rules of the Joint Entrance Examination Advanced, you have to compulsorily attempt both the papers in both the shifts to make yourself eligible for the results and the counselling process. If you don't appear for the second paper and leave after the first, your result will not be published and you'll be marked absent as a result of which you'll not be able to sit for counselling or get admission to colleges on the basis of your JEE Advanced marks.

Hope I have answered your question. All the best!