If secession ever succeeded (unlikely), I predict an exodus of another wave of tax-paying residents of the Golden state. Many have left already.
Cali would have to couple secession with instantly sealed borders somehow to prevent anyone from leaving. As a seperate “nation” the coastal industries of the superrich would not have much of a domestic market for their wares and anything exported to the US would be subject to trade restrictions and whatever tariffs the US imposes. Their industries would probably be lining up to move either to Asia or to the newly deregulated and tax reduced US.