That would be a problem I didn't think about. If the secession movement was regional within the state and, for example, the Gulf coast area voted overwhelmingly to stay and the rest of the state voted overwhelmingly to leave then what do you do? Would Texas be willing to split off that section ala West Virginia and allow it to stay? Does Texas drag an unwilling part with it? The whole concept is fraught with peril.
FWIW, if Texas were to split into 5 states, there's no guarantee that all those states would be Republican. South Texas and West Texas might not be. Not so long ago, East Texas was Democrat country as well.
Texas can split into 5 states or 50 and unless Congress approves then it isn't anything but one big lump of a state.
Given how traumatic that would be for Texans, I don't see it happening. But an independent Texas absorbing other states or territories ... that could happen.
I don't see it happening either, with Texas or any other state. All the secessionist who are hell bound to leave the U.S. will have to find another method.
I just want to be free from you, politically speaking. The only peril would be from an invading army led by Federal Bootlicking storm troopers like yourself.