Os livros ainda não chegaram tão longe. É provável que este seja o próximo romance " The Winds of Winter " (que tem o mesmo título do episódio final). Então, não posso ajudar a dar uma resposta dos livros.
Do ponto de vista do show, no entanto, Lancel ter seguido um dos "Little Birds" nos túneis sob o Sept nos deu uma idéia de como a explosão foi montada e como aconteceria. É provável que Lancel tenha morrido de qualquer forma, no entanto, tê-lo levado à adega do Sept não só dá aos telespectadores uma idéia da escala da operação, mas também mantém viva a possibilidade de que Lancel possa salvar o Sept e todos dentro .
Esta resposta é muito opinativa, já que é o episódio final da série de TV, e ainda não foi mencionado nos romances.
No entanto, consegui encontrar uma entrevista com o ator, onde ele discute um pouco a cena:
What was it like crawling through the corridor?
The thing about the whole scene was that for the last two years, we’ve seen Lancel be this stoic, disciplined, focused individual, with a rather limited demonstration of much emotion. But when the worst happens to him, and he finds himself staring death in the face, he tries to do his utmost to solve it. He doesn’t give up. He doesn’t cry. But he is, for the first time we’ve seen in a while, really brave. He wants to make sure everything he’s worked for doesn’t go up in flames. And having just suddenly been paralyzed, and being on his own, with no one around him, he would probably bleed to death anyway if he didn’t get the candles out in time. And yet, he still does his best. I found that to be rather emotional, because for all of his bad choices, all the bad things that have happened to him, he still tries his very hardest to do what he believes to be right. And that made him vulnerable again. I could have played that entire reaction very robotically, the way he’s been. But instead, I let him cry out in pain and didn’t deprive him of his humanity. He was still human. He was scared. He didn’t want to die. But I am glad that my character has died the way he has. It was quite a cathartic experience for me.
Vulture.com: Interview with Eugene Simon