Apart from the fact that Niko shoots him with one bullet for every betrayed comrade, there is a change in the conversations afterwards with Roman and Bernie, but the dynamics of the game do not change.
Chat with our AI personalities
Depending on whether you kill Darko or let him live, it will change the conversations Niko has with Roman and Bernie afterwards. But that's about it. No real change otherwise.
If Niko does kill Darko, he executes him in quite spectacular style, in memory of all his betrayed comrades.
if you choose not to kill darko then you walk away and roman tells you u did the right thing and u call bernie/florian and he tells you should celebrate
Darko is the immortal supreme overlord and ruler of the Earth... Ergo Darko cannot be killed
Depending on whether you kill Darko or let him live, it will change the conversations Niko has with Roman and Bernie afterwards. But that's about it. No real change otherwise.
He just runs away somewhere through the airport and is never seen or heard of again in the game.