I get you. But I feel I all three were walls that he had to overcome. N if he doesn't kill Miss Mage, she'll probably be after his ass once he gets into the enemy city/camp. Plus I'm sure he just wants to grow stronger (^_^)
That's how he is, his obsession on conquering things that made him despair is what led him to this situation. Also, even if he didn't seek out that made, she will still be problematic. Who knows if they go through the tunnel, the mage might follow suit and they will still end up dead so it's much better to eliminate all possible dangers if he have a way and have a better advantage on knowing the near future, much better than getting nervous at what will comes next because you left a danger alone on it's own devices
Miss mage has a spell in the cave shed come at them if she finds anything sus
So a surprise attack would be more effective, plus fighting her in a narrow cave will be suicide
I have to say
He's really insane and reckless and a quite a little shit
(I say this, but don't be mistaken, he's *loved* by me)
My point is
Did he really have to seek out Miss mage? Couldn't he use the tunnel now that he killed captain Roger and his squad? Why would he put his life and his friends life in danger, out of greed, really