In Zamboni's original research, it was 50% to 50% between the patients who had veins that stayed open and the patients who had their veins close. This research has not yet been duplicated but those percentages were what prompted Dr. Dake to use stenting. Stenting may be more effective at keeping veins open (remember, stenting is susceptible to in-stent stenosis and there is a possibility, hopefully small, of the stent clotting over and permanently closing off the vein unless it is cut out surgically). Dr. Sclafani has experimented with a cutting balloon that has been shown elsewhere in the body to reduce the risk of restenosis. But almost anywhere in the body where angioplasty is done, stents are used as well. They are cautious in the neck because of proximity to heart and brain and the lack of a venous stent.
Anyway I think the short answer is the one I began with: 50/50 chance of veins staying open; but if they close, being retreated with ballooning a second time may keep them open or maybe at that time stents would be used.
"However, the truth in science ultimately emerges, although sometimes it takes a very long time," Arthur Silverstein, Autoimmunity: A History of the Early Struggle for Recognition