What if Major General David Twiggs never surrenders his command in Texas. Does he have a chance of holding out? Does Texas manage to succesfully withdrawal from the union or not? If their were battles, were would they be?
Short answer - no holding out, no "independent" Texas. Texas does not have the manpower or industrial base to continue fighting. All that Twiggs holding out does is cause more death and suffering, mostly on the Confederate side. Also, you'll probably see a larger Union postwar occupation of Texas since there will be a larger Union military presence there when the war ends.
The Op is not talking the end of the ACW, he's talking the beginning, when Twiggs as a Union general surrendered his entire command to the Confederates.