The Mexican deportations worked as well as required at the time (they were never intended to remove all of them). The reason there are heaps of Mexicans (and many others) in the USA today is because of the 1965 immigration and nationality act.
If they had removed every Mexican by threat of death in 1964 and then introduced this the next year, there'd be a lot less, but still probably close to 20m Mexican Americans.
Spain is currently handing out citizenship like it's candy.