Soon-ae spill everything to Soo-ji in the car. Meanwhile Do-han sped himself to be the first one arriving at 1080 Buam-dong (address from the scheduled text). He did a site check and informed Eun-joong, asked for back-up and be prepared for stuff falling from rooftop (because duh, it’s Shi-wan). He sent a text message (which is the next most natural thing to do if you cannot reach someone by calling, for goodness sake!) to Soon-ae telling them to stall, stall, stall while Bo-mi & Kyung-soo continue the search for Se-won, and left before Shi-wan arrived (assuming the little creep was going by bus or some other public means, y’know, mom got the driver and all), backtracked and fake-followed them for Shi-wan to see later.
So when Soon-ae and Soo-ji arrived at the building, they play-acted and the scene unfold as is. Except, when Do-han & creep fell, Do-han landed safely due to Eun-joong’s preparation (maybe a super big air mattress… still a bit fuzzy here but have total faith in Eun-joong’s ingenuity). Shi-wan hit hard concrete with a thump but survived, and paid for his crime by being paralyzed from neck down. Soo-ji & Se-won visit him in the hospital and told him they pity him; naive Se-won was sincere while Soo-ji did it for the fun of watching the creep seethed helplessly.
And Do-han, of course he faked his death! He faked a death before, why not his own (insert smirk here). He moved to the suburb with his father after getting an impeccable new identity from Kyung-soo, and be a devout Catholic and goes often for “confession” in the one church we all know. In the sequel, Soo-ji is the field agent, Kyung-soo & Bo-mi are the snoop agents where missions double as dates, Eun-joong is their lawful hand of justice, Soon-Ae and Jin-ki are their collaborators within the police, and Do-han is the unseen brain. And he can man the CCTVs too.
(Ok, now I know why people write fanfiction!)