I have been thinking of this all day, how would I write his demise. I honestly never watch horror stuff. So I have debated and think it would work if Konstantin was trying to kill John and it backfired and he did himself in. All by himself. So how? First, Konstantin has to learn that John did not actually kill Konstantin's daughter. He was out of it, being controlled at the time.
The daughter tried to help bring him out of it. Konstantin got upset, came to shoot John, daughter came, knocked Daddy down, his gun went off, she died. Steve walks in, evidently, Konstantin on the floor, dead daughter on the floor, brainwashed John having fainted or in a trance or something. Konstantin comes to, convinces himself that John is at fault. But takes 30 years to seek revenge. Ahhhh, there's the rub.
Konstantin had wiped it all out of his mind, putting in the scenario that John was the guilty one. But he could not escape the truth. So when confronted by Steve, with Harris & Jada along for backup, Konstantin takes off, up to the rooftop, Steve, Harris, Jada, John, in hot pursuit, where he throws himself off the roof, rather than face the music.