nice EAT Sandeep for an equally great episode. Yes the decoupling was a bit out of order but still we can ignore it. the plan was to kidnap HD and succed in getting more info about the national security issue while the whole world will believe that HD is died in the blast. the moment his comrades / gang come's to know about his death, th BK & Sandy are expecting some of his people will come out of their hideouts and try to act smart. In other words, they are expecting his people will start abusing the government or act violently which will give the officers son=me hints about his gang and what they do in reality. As of now, they only know that HD helps some terrorist groups financially but apart from that they have no proper info. So this plan to kill HD is to make the rats come out of their holes.
BK was casual as he was assured that Sandy is safe along with HD while in reality the Naxal head who would have suspected Sagarika would have kidnapped her along with HD (saving HD). May be he is not aware of the truth that Sagarika is Sandya the IPS Officer, he must suspected her for kidnapping HD while HD is still unconscious, so he would have ordered his people to tie the lady. So later when HD come back to consciousness, he may reveal the fact that she is his fianc and they were going to the temple. By then they might get the news about HD's death alog with Sagaria, Shanatanu das and many more (as per railway booking list). So for some reasons, they may stay hiding for some time and BK will be thinking why Sandya is not contacting him yet.