The blue fire was raw, wild magic, unbound from the Weave at the time of Mystra's death. It's effects were unpredictable, but often lethal. Spellscars were uncommon, and not always the result of direct exposure to Spellplague. Some people simply developed them.
*******SUNDERING NOVELS SPOILERS FOLLOW*******
How does one use spoiler blocks on this site?
We actually can say with near certainty that all Spellplague has been purged from Faerun. No more Blue Fire. The cleansing happened in one of the Sundering novels, and was the result of one deity figuring out a solution, and then collaborating with another to enact it through the actions of their Chosen.
There would still be Spellplague before this event (in 1486 DR, if I remember correctly). One of Bruce Cordell's post-Spellplague/4E novels had a character awakening after a century trapped in crystallized Spellplague, for lack of a better description.