As improvement occurred only several months after infusions were given I think it's unlikely that any outcomes measured an actual effect of Saline IV or volume expansion?
(Apologies -- in skimming-mode only so in case it hasn't been discussed in this thread yet: How could there be any long term effect of volume expansion via infusions? Wouldn't you need to receive them daily?)
I wouldn't rule it out. I just don't think we know enough as to why saline is beneficial.
I mean it directly improves the functioning of the vascular system. Repeatedly pumping up the system may be enough for some people to get to a better level of functioning.
This is too speculative though, point is that it's worth studying to characterise its impact.