Modern development of California began in 1849's Gold Rush and was an American, not a Mexican phenomenon. Like Texas, it broke from Mexico and became a Republic before joining the Union.
Aztlán is a Mexican fairy story. Neither the Mexicans or the Spaniards before them had more than the barest scattering of settlers in the Southwest they sold to the US and barely scratched the surface of its potential.
BTW, you'd be hard-pressed to find any group more opposed to massive immigration from Mexico than the descendants of the few original Spanish settlers in places like New Mexico. The Spaniards ... and then the Mexicans after them neglected the settlers and left them to wither on the vine, crushing any attempt they made to assert their rights. The Mexicans even crushed the missions, a key economic engine of their colonies.
Return? Bullshiite.