Don't believe for one minute that Vicente Fox and his fellow corrupt elites in power in Mexico would have the "guests" return in 3 years. Imagine 25 million Mexicans heading back home --- Fox would be angry as hell.
I do not see a lot of love going on right now.
Besides, Fox is being voted out soon. The next guy is likely going to be worse.
Returns will be staggered, and this process is going to take years to complete. Perhaps as many as ten. Over that period of time, it will not be as you fear. Those not able to be matched with jobs for security reasons will be deported first, as they will not qualify.
This would be very gradual, but that would be somewhat deceiving, as the numbers are huge. They will be working their asses off.
But hell, it won't be anything unless we do SOMETHING.
Right now, I see no chance of doing anything at all except painting more lipstick on this pig we call the immigration code.