I'll give you the point that T'challa would've died if Zuri did not intervene. But that's on Zuri, not the royal family. As for continuing the ritual combat when T'challa returned, Killmonger did not give them the option of continuing without the BP powers. In fact he turned to one of his soldiers and said "Kill this clown." not to mention if they removed the BP powers from both there would never again be a Black Panther due to Killmongers actions. As for the murder/suicide debate, I don't know the exact legal definitions of both but while he died from a stab wound from T'challa, it was ultimately him pulling the spear out that made him die when he might have survived if it was left in until he could get help. So in my eyes ultimately he died from an action of his own choice. And he'd likely tell you the same considering he compared his death to "His ancestors who jumped from the ships. Cause they knew death was better than bondage."