It cannot be peaceful.
If 51% are for secession what are we to do with the other 49%? Are you going to make them leave? Are they not still citizens of the United States?
If you want to pretend then I will impale every fuging terrorist/secessionist with poison tipped unicorn horns.
again, if secession was a reality, then it wouldn't be anything close to a 50-50 split (hence the severe improbability). such a circumstance would only exist with a 10% minority at best with the likelihood of mass migrations across borders both ways. there could even be resources dedicated for both nations for relocation purposes as real estate agents would love the boons to their businesses.
i realize you are trying hard to reject the premise to derail the intent of the OP, but the fact of the matter is that this notion has gained steam in the past decade. it certainly isn't a reality now, but it could become much closer to one as the dollar tanks with runaway inflation in the coming decades.