California leaving the Union has little to no chance of happening. The state is one of the most liberal in the entire country, and it isn't surprising that many residents want to leave the United States after Trump was elected. While many are calling for California to secede, there is a process for it to happen, with a two-thirds approval majority needed from both the House and the Senate. If you remember, Texas also called for secession during President Obama's re-election but nothing came of it.
IMO, the Republicans must support the secession of California from the United States. There is no point in holding on to CA, as it is almost certain that the state will be having a Mexican majority in the near future. Also, the secession of California can save enormous amount of tax money, which is currently being spent to subsidize the welfare rats there. Imagine what would happen without the 55 electoral votes from CA. The total number of electoral college votes gets reduced to 483, with 242 needed for victory. The repubs can afford to lose all the swing states.