S7. Why can’t Aarvos be killed?

If Aaravos once said that “a starlight elf can only be killed by an arch dragons bite” “In the woes of death the dragon perished as well” “a tooth was taken and novablade was created” Sol Regem is behind them. Can Ez not just rip a tooth/teeth out of the arch dragon and stab him with a ballista?!?! This is a serious question because it’s not like the archdragon has to be alive.

Thank you, enjoy this picture of Rayla