For those saying people will leave, I'll note that I first heard that going on 40 years ago in a Wall Street Journal article that talked about how California's high tax rates were driving people to Nevada (now, why I remember that...?) I'm sure that the WSJ wasn't lying, and some former CA residents did, indeed, move to less taxed states. I've heard the same trope repeatedly in the years since. I'll note that the complaint most folks have with CA these days is the cost of housing, indicating that taxation didn't drive everyone away.
My understanding is that both are true; net interstate migration is away from CA, but CA's population is increasing due to international migration and relatively high fertility among some communities. On average, CA's emigrants are richer than its immigrants.
The high tax rate has the opposite effect that most people seem to assume. It attracts and concentrates high-earning people, because they're the only ones who can afford it. If you look at migration stats the category of California residents that grows is the top income quintile.
