Sometimes the joints between the sections are not at the newels, as you might expect, but halfway between newels. If so, the sections can be easier to take apart. Perhaps not likely with that design, but worth checking.
If the joints are in the newels, there will be a way to get them apart, but it will be a filthy job to do in situ if it’s all corroded in and everything will need freed up from the base to allow a bit of movement.
Sometimes lead was used in the joints, particularly if the balusters were set into a bottom rail.