End game spoilers below.
Roman doesn't die if you don't want him to.
One of the very last missions gives you the choice of helping Dimitri and thus earning a huge reward, or taking revenge and killing him.
Be a pusillanimous individual and work under Dimitri = Roman will end up getting killed.
Be a man and kill that slimy forget = Kate dies. She was a stupid ginger that never put out anyway.
She dies because Jimmy wanted you to work for Dimitri, not kill him. He comes to Roman's wedding and shoots her while trying to kill you.
Summery: Roman doesn't die.
A guy on another forum spammed "ROMAN DIES" all over the place. I was pissed. Towards the end of the game I was like, "Man, I bet Roman dies soon." Never happened. Woohoo!