I despise illegal immigration, but any talk of Texas, California, etc trying to secede is nonsense. As the Civil War showed, secession requires a great military force. The South had an outstanding army with able generals and still wasn't able to get it done.
Hispanics WILL have a political majority in those areas very shortly, but in the current American system being in the ethnic majority doesn't mean a hill of beans, legally speaking. The current situation of white Americans, legally disadvantaged by racial quotas, etc. certainly shows that.
Finally, I'm skeptical about how militant against white people the average Mexican actually is. The fact is, Mexico places the white citizens in its own country on a pedestal- most of the anchormen, actors, politicians, etc are white.