To start with the Filmmakers have created an Open Ending for #sacredgames.
But My Version of Ending would be that Bomb didn't get diffused. Even though the probability that Passwords were different to Activate and De-Activate,I still think that Sartaj didn't De-Activate it successfully.
Coming to the why part, As you could observe Sartaj was way too deep into the cult and the teachings of guriji, when Batya says 'Give me One Reason to Save the World' and Sartaj is very unclear about that answer until the extremists gang (including katekars son) beat and kill the boy in front of his very own eyes. That Moment is the defining moment in Sartaj life as he is convinced that this world is beyond repair.
When Batya says the Sartaj had Cosmic connection with Gaitonde, she literally gives him the mantle to find the book and lead them to satyug, As Gaitonde drops the plan. This is the sole reason why Malcolm Murad doesn't kill Sartaj when he meets him as he clearly understands that only Sartaj can find the book and lead them to Satyug. Malcolm Murad ends up giving Balidan.
The ending very cleverly draws two parallels between Gaitonde and Sartaj. On one hand Gaitonde kills Jojo and Sartaj has placed the Trigger on Batya on same way. Gaitonde kills Jojo and tries to save Mumbai and on the other hand Sartaj leaves Batya to make sure Batya and remaining people achieve Satyug. The Most Important Detailed to be Observed is when Sartaj leaves the bunker trying to find the bomb, He makes sure the Bunker door is Closed which implies he wanted to save Batya and the people in the bunker. If he really wanted to diffuse the bomb he wouldn't have closed the door implying that even if he failed then nobody should remain. Also clearly observe that Sartaj says aham bharamsam when trying to use the last chance which clearly states that he was way too convinced by Batya.
Now coming to the Pattern, It couldn't have been Dilbagh singh password to deactivate because, only Dilbagh was unsure to give handprints to guruji and guruji must've make sure that to deactivate it, Dilbagh password is not used as it is very easy to crack which connects to the end scene where Gaitonde telling Sartaj (when entering dilbagh singh password) that 'If it was this Easy then He wouldve only done it' which implies that guruji wanted to make the bomb fail safe.
The Ultimate connection here is that Gaitonde was the man to lead them to Satyug according to guruji and for Batya it was Sartaj. This implies that Gaitonde and Sartak led 2 different paths but were connected. Gaitonde first wanted to destroy the city and then save it, whereas Sartaj wanted to save the city first and then destroy it. So guruji and Batya make sure both their Savior's end up sacrificing their Life for their Mission.
