If Scar were still alive, Zira would still be alive and happy, Nuka would still be alive and most possibly happy, Vitani wouldn't have betrayed, and Kkovu wouldn't have betrayed. I see them as one of the happiest families in the movies. If you think about it, everyone in this families destiny's are connected to Scar somehow.
Originally he was going to be but they had to change it so that Kovu and Kiara wouldn't be cousins. As to whether it was confirmed about him not being the father to Viatani and Nuka, not a clue. In the movie we only know that both Kovu and Nuka state that Scar "wasn't even his/my father"
A family torn apart by the evil and greed of Dark Rogue Simba. They're youngest shall rise a rebellion. His parent's hearts shall always be in ours. Oh wait. I'm pretty sure zira survived. Just voicing my thoughts