It’s obviously Gaban cut off Imus arm.
I mean, if Gaban lost an arm already, someone or something relevant enough will need to show up to back him up since Luffy is done and too weak rn
If not, then Gaban, without an arm, will still keep fighting until someone shows up to help him or Zoro and Sanji defeat the HKs
Which ends up in Gaban glaze, since fighting without an arm and out of his prime would be insane
Or its simply Imu who lost an arm but he can probably regen that shit (most probable option)