The thing is who are those fleeing from California - if they are the ones that reliably voted Democrat since the 90-s - then you should be scared of them flipping Texas blue if they want the same policies that lead California to its current messiness. If those are disillusioned democrats that actually want different set of policies - it is different beast, but I haven't actually seen good studies on the matter.

Prior research on this, at least in my metro area, found that most people leaving California for Texas were doing so primarily for financial reasons. The research could not identify any political leaning for these people as they seemed split down the middle.