Hints Balli is actually Karan in today's episode:
1. Balli trying to comfort Faizi over Karan's death. Karan is very close to Faizi and use pata hai ki usko kya bolna hai taaki use thoda better feel ho. He didn't want to see him in pain, toh isliye yeh kaha.
2. Batra Sir saying 'Mere Karan ko waapas le aao.' I feel Monami ko bhi thodi ajeeb lagi yeh baat. Even if Monami agrees to pretending about Balli (which she did), usse Karan toh waapas nahi aayega (if he was actually dead.)
I feel Batra Sir ko pata hai ki Karan zinda hai. Ho sakta hai he doesn't want people to know about Karan 'dying', in the academy, because he doesn't want to cause more grief. He knows Karan is a very loved person. Wo yeh toh nahi bata sakta ki Karan is actually alive (because if it reaches the wrong ears, it'll jeopardize the mission) even to people closest to him, but jitne logon ka pain kam kar sakta hai, utne ka kara hai.