In 白銀のソードブレイカー vol. 2, by Matsuyama Takeshi, I found this sentence:
もちろん、エリザの病気を剣聖に診てもらうわけにはいかない。もし身元がバレたらそれまでだし、そもそも『処女神拷問{アイゼルネ}』を直さぬかぎりはエリザの回復もないからだ
処女神拷問{アイゼルネ} is Eliza's sword, and previously it broke; the sword is linked to the girl's health, which began to break down as soon as the sword broke.
The Sword Saint is a girl with a magical sword that can heal wounds and illness; that sword could repair Eliza's, so the main characters are on their way to a meeting where the Saint will heal people with the goal of stealing her sword.
To make things worse, Eliza is wanted, so they really can't reveal themselves and are posing as brother and sister.
I think I understand the gist of that sentence: they can't have the Saint check Eliza, she could be found out, and she wouldn't be healed anyway if her sword isn't repaired. But I'm not sure about それまでだし: I tried looking on this site, my grammars and a bit of googling, but came out empty handed.
