??? No, Kusakabe & Higuruma simply talk that it isn't impossible for a curse to grow stronger when someone dies. They are talking about the fundamentals.
Correct. But before that flash back Higuruma thinks about his "role" in this fight.
"I'm intent on fulfilling my role and dying."
K: "Curses don't always weaken after death."
H: "Yeah, the general idea is they get
stronger."
H: "My role."
Then it shows Nanime's death as Higuruma passes his gavel to Yuji, "You've got it from here." ie. Another character passing the torch to Itadori.
It's quite explicit by the end of 247 that Higuruma had decided that if he died it betters their chance of killing Sukuna.
AND then it doesn't actually work. So either he sacrificed himself for no reason, or he isn't actually dead, or the effect of his death hasn't been felt yet OR, it simply represents narrative growth of Itadori, who cracked at Nanime's death but now has the conviction to continue fighting after losing another friend.