"Could USA become split up with certain states moving away from centralised control? "

The standard answer is 'we tried that in 1860s, result was The Civil War' and at least 620,000 lives lost.

That said, times change. Since the federal government has become an expensive and irrational loose cannon in the nuclear age, perhaps there is a scenario where the 50 governors (well 52, let's pull in poor DC and Puerto Rico) have a confab. Say they agree to cut the US into 4-6 new countries, see if the state legislatures will go along. They could all spend a hot summer in Philly working out the details of who keeps what in the divorce.

The nation only exists as 'a sacred union' as long as everyone is willing to play along. I don't think in these times that anyone sane and under 30 wants to march to war to stay wedded to Oklahoma, and few in Oklahoma will be sad to see California go.

As far as preserving the union at all costs, the founders made it abundantly clear they EXPECTED the people to throw off unjust rule.