Another thing is he is also a believer of inherited will like he is a big fan of Davy Jones, so when he dies, he should know someone will inherit his will.
especially considering Rocks' "I'll be back," line to IMU. He's more into the inherited will stuff: he knows that if he fails, his desire to see the world toppled (which was Davy Jones' desire as well?) will simply find another conduit to occur further down the line. IMU can delay it all he wants, but it will happen: MJ & the WG will fall.