I get a feeling the empire is a total amateur at this whole espionage, subterfuge, and assassination thing. Wasting that guy for this sort of stupid operation was a huge waste, and he isn't good at it either. However, he was quite good at simply being there as an infiltrator, so he could have kept providing the empire information from the inside during an open war, perhaps at a crucial moment struck from the inside with a few other people. Just once.