My biased fanboy wish:
Momo holds onigashima first, everyone is celebrating him, he is happy he managed to do. Kid hears his inner voice becoming more silent and jumps into the hole in Onigashima.
A few moments later, Momo faints, it was to much. The island is falling again, everyone panicked, until it suddenly stops.
Kid stands on the ground of wano, arms in the air like genkidama. He is bleeding out of his wounds, eyes, nose, mouth… and says:
„Law, get them out of the island, I can’t do this for long…“