texas used to be isolated from the rest of the US electric grid for exactly this kind of reason. But I think a decade or so ago California forced Texas to connect so they could take power they needed.
The bulk of the Texas grid still is isolated and run by ERCOT. Texas has three HVDC interconnection points a north ,east and the railroad HVDC they can only pass about 500 megawatts each so a drop in the bucket compared to the 85,000 megawatts ERCOT capacity.
Texas is also not in synchronous to the Eastern or Western interconnects the 60hz of the Texas grid is not the in phase with either the East or Western interconnects so AC-AC connections are impossible. It would require a black start event in Texas on purpose to sync the grids as in a total blackout then start the Texas grid with external power and frequency control from either the Western or Eastern grids. In other words never going to happen. There is a small 100 megawatt variable frequency transformer in the Del Rio area that allows Texas to shift 100MW to and from border Mexico by shifting the 60hz phase to phase with the Mexico grid. There was a plan to build the three sisters HVDC grid tie in the Texas panhandle this was to be. Very large 5000 megawatt three way HVDC TO HVAC bridge the cost was in the billions and Texas would lose its exemption from Federal DOE oversite the voters put the stop to it with legislation post haste.