Sandhya?

Why is Garjana keeping Sandhya alive? (especially she could stop the project!). And it is clear whoever else is involved in "IPS" officer's operation!

Sandya is kept alive by GS not because she is the heroine but they need to get the information about what all the secrets she has already shared with her team, so that they can make alternative plans. Otherwise they can't go ahead with their original plan if the Govt has already prepared for the same with counter plan. If they had to kill her, they could have killed her the day they caught her and there was absolutely no need fro them to keep her alive till now.

And also they want to know about the remote which sandy hid. They want to make sure that the remote hasnt reached the police yet as that can be a problem for the mission as well.