Speculations If Luffy doesn't kill...

[moreha9685]

They'll have a full on fight and Imu will die in a volcano or drown in the ocean or something like that that.

For a character who lives in the shadows, travels by black magical circles, and acts like the devil incarnate, IMO Imu should "disappear" vaporized by sunlight.

 

[Owl Ki]

For a character who lives in the shadows, travels by black magical circles, and acts like the devil incarnate, IMO Imu should "disappear" vaporized by sunlight.

Luffy gonna punch a man so hard, he flies into the sun.

 

[moreha9685]

Luffy gonna punch a man so hard, he flies into the sun.

Or, Imu falls into the neverending day under Enies Lobby

 

[BoaHancocksHusband]

Talk No Jutsu and a game of Scrabble

 

[smallpecker84]

Luffy is like Batman, he does not explicitly kill. Its still entirely possible villains die from other bullshit if Oda deems it so. Imu will probably drown after Luffy refuses to fight him anymore or some shit like that.

 

[MonsterKaido]

Imu will be sent to a moon where they will be sealed forever or outer space like kars from jojo.