Complex sentence: As he doesn't want anyone to find out what he's doing in the mines, and hopes to keep them secret until Kycilia takes over, he decides to sabotage Ramba, who already knows too much.
Split into simpler sentences: As he doesn't want anyone to find out his activities in the mines, and hopes to keep them concealed until Kycilia takes over. He comes to the decision to sabotage Ramba, who already knows too much.