On the subject of this administration following the law of the land, it seems they are selectively doing so when the law supports a position they've taken. Usually one that increases their power/control of the rest of us.
I wouldn't bet money against the Obama administration prosecuting anyone felt to represent a threat to their control, to the fullest extent possible. Remember the whistle blowers recently in the news:
That said, I doubt much serious federal action would ensue if a state like Texas decided to secede. You would probably see things like air travel curtailed until Texas by cutting off hydrocarbon changed the feds mind about continuing such.