Luchen Rhayell, the central figure of the rebel network, is the only person who knows the truth about the rebellion and knows how to deceive the Empire.
The ISB was unable to verify the truth of the rebellion, and the Emperor was dissatisfied.
No matter how strong the orders from the center, they will escape. The Empire at that time was unable to control sporadic rebellion activity and it was difficult. Dedramiro alone cannot win.
However, relying on Lucen alone is actually dangerous.
Until now, the rebellion had been carried out on the assumption that Lucen would not fall into the hands of the Empire, but all of that will be overturned.
The rebellion will be revealed one after the other, and the ISB will be able to uncover the truth about most of the rebellion. Mon Mothma will also be arrested. The Emperor will order a purge.
I think Cassian will probably eliminate Lucen, who has fallen into the hands of the Empire. It's a difficult task, but it's necessary to keep the network a secret from the Empire.
By eliminating Lucen, they will bury all the secrets and outwit the Empire.
I think Lucen himself had a vague feeling that he would be eliminated in the end.
He holds a lot of secrets and information on his own, and is a dangerous person. And he has been deceiving the Empire. Lucen wants to achieve the Rebel Alliance even if it means sacrificing himself.
This will save the operatives that make up the network Lucen has built. But those operatives will not be aware of Lucen's death.
(The ISB may force the Empire to reveal its deceptions. The idea of decentralized governance and sporadic control would eventually develop into the First Order plan.)