Eventually, they will wise up, move out of their expensive rentals and turn frugal - likely outside of these cities with a good possibility of leaving the state.
In their absence, new young folks in their high-earning high-spending phase will move in, and the cycle repeats itself.
None of this is bad for California. The state, in the desirable cities, is a meat grinder drawing in a constant supply fresh, gullible, overpaid talent, working not just to pay high rents but high everything, including state income tax, while saving very little. When they get exhausted, they leave, and make room for more fresh meat.