Preditction time:
Saturnmu is about to defeat Kaido, Whitebeard and Xebec. But, realizing that Xebec would be a good asset to them, Imu either forcibly turns Xebec into ademon, or makes a deal with him.
This then leading to Roger and Garp supposedly beating Xebec as Sengoku said.
From what we know about Xebec, would make sense that he would neither be prideful or idealistic enough to just rather die than bow to Imu. Especially if imu does some shit like saying "I know you have a child. One of your own betrayed you. Serve me, or I will hunt both your kid and wife down" or something along those lines.