what is the possibility that this topic will lead to world war 3?
There is zero chance of this leading to some huge conflict. Flat Earthers can't even agree on every aspect of their own model; they basically just agree the earth is flat, and everything else is kind of just up in the air and doesn't really matter. Prove any aspect of their beliefs wrong beyond all doubt, and flat earthers will simply ignore it and spout some other flat earth nonsense ad infinitum. The various flat earth models that do exist contradict both themselves and each other in countless ways, and every single thing that can't be explained or reconciled by a flat earth model is reconciled and understood by science in a consistent model of a spherical earth. Flat earthers never seem to be able to distinguish between proof and imagination (e.g. Flat earthers think that simply making an illustration of how the sun and moon might work wth a flat earth is proof itself, etc.) nor do they understand that their conclusions don't flow from their premises (e.g. you can't freely travel Antarctica as you please, so the earth must be flat, etc.).
Flat earthers live in a bubble where proof doesn't matter, logic doesn't apply, and where their beliefs are reinforced only by other bubble-dwellers, a group consisting of Internet bloggers and religious fanatics with little-to-no understanding of science, mathematics, or logical inference. Nobody takes them seriously except themselves, and they constitute only a small minority of people.
The end game for flat earthers is already here: terminal ignorance.
You speak in Darwinistic like terms, you don't think those that know we live under an artificially constructed dome have a technological advantage?