Yu Yureka Black is always booting into TWRP (Fastboot Not Working, No OS)
if u have already unlocked the boot loader, u already lost all the data.
To unbrick, get lineageos 14.1 garlic from http://download.aosparadox.org and flash it via twrp. it is not advised to use qfil unless your is hardbricked. follow this tutorial to unbrick using qfil http://forums.yuplaygod.com/threads/guide-unbricking-yu-yureka-black-reviving-from-dead-and-restoring-stock-marshmallow.49751/