"What makes you think he'd succeed any better with a loss of an only son?"
Because he has a daughter, and Nala and Timon & Pumbaa are right by his side, and that it's over now, not to dwell on it.
Anyway, I think that even if Kopa did exist, they would've excluded him from SP because it was supposed to be a story about Kiara and Kovu; Kopa (All 3 of their names start with K?) would've had absolutely no signifigance to the story, and it would've been confusing to the audience. "Who is this strange lion?"
There is another popular theory; Kopa does not want to be King and so runs off to form a pride of his own, much at the discontent of Simba (Of course Simba didn't know about because Kopa didn't tell him and ran off while Simba is asleep)
You're not changing my mind, man, I still support Kopa as canon
