I don't think secession will happen, but if it were to happen, it will be more along the lines of Scotland's attempt and Brexit; a long drawn out political process that will rival the conference realignment in fantasized combinations and permutations. In other words, there will be OR/WA joining California (safe bet), Phoenix area trying to dump the rest of the state to be with LA area (similarly TT latching onto UT), the red portions of CA/OR/WA whining like Nebraska/aggy but knowing that they are net takers and hence better make a deal they don't deserve to be part of the blue coastal coalition, the immediate red neighbors (AZ/NV/UT/ID) seeing the future on the west and literally nothing to their east will try to form an independent coalition while trying to have a most favored nation deal with the west, the midwest desperately trying to hang-on to the northeast, and the south happy to be what they are and proud of it (better 155 years late than never for them). This leaves Texas to form its own coalition out of NM/CO/KS/OK.
Again, it won't happen, but if it were to happen, it will long and messy, and will be a political dissolution rather than an abrupt civil war, IMO.