I actually think that the GOP will be the bigger problem in a secession scenario. TX has 38 electoral votes. If those were to go away, it would mean permanent minority status for the GOP.
For me the issue is what is happening at the state level. States will have to decide what is best for their futures. Many states suffer from unfunded mandates and already find the federal tax buden is unsustainable. High-employment states, like those in the South are carrying the load for more liberal states.
Taking the producing states and their tax revenues away only worsen the burden for the more dependent states. It forces the other states to make very big decisions to go Left or Right.