The title says it all. Lets pretend that Rockstar would give us a choice between killing Vince and Tony during this mission. Kill Vince, you get the regular happy ending, kill Tony, you get a different, sad ending. What would it be in your opinion?
As it goes for me, I think it would end the conflict with the Ancelottis, but the Russians would still come after Luis. After wiping out the assassins in Maisonette, Bulgarin would end up kidnapping and killing Luis' mother and Henrique, leading an angry Armando teaming up with his friend again for good and they end up killing Bulgarin. Not much of a difference but it's a sad one, knowing you did the wrong choice.
This doesn't rule out the possibility of Rocco not appearing in GTA V, he may still skip town because he doesn't see any business opportunities in Liberty.