Let Me Rest, Please
When the bomb exploded, the body of the Secret Society member too vaporised. But, it wasn't his true body. The true body was the Invoked Spirit seated within the Dreamland, one housed within the soul-mind combo of their body, almost akin to being in a different dimension.
And hence, even when the body was destroyed, the member wasn't dead. Once the effects of the explosion vanished, the member appeared in his Invoked Spirit form and then expended some Mental Fragments to create a new body.
Compass Carburettor was huddled in the Dreamland where the rest of his group was residing, braving the attack.
Following that, he retracted the member—with the power of the Bomb—into his body and then transformed into the truck that slammed into the Waning Essence System, reverse transmigrating it to the System World.