I don't pretend to understand what a fluctlight really is, but it seems that since it can be transferred into a computing environment, it could possibly be created.
I was also thinking possibly the old data from dead people that might have been stored in NerveGear, AmuSphere, or Medicuboid could be used to bootstrap a new fluctlight. Even in the SAO world, there doesn't appear to be the technology to insert a fluctlight into a body (but I haven't read enough, so maybe there is?), but if you could create a fluctlight then someone could be semi-reincarnated inside a virtual world...
Any data that may have been stored by any conventional FullDive machine (if they actually even have that capability) would be FAR from sufficient to create a Fluctlight out of it. The Soul Translator, the only machine that can interact with Fluctlights so far, works on an entirely different principle than any FullDive machine before it. A regular FullDive machine just scans the electrical activity of the brain; the Soul Translator registers what photons within the tubules of the cell are doing. The former basically just gets info on what the brain is thinking at a given moment, the latter essentially scans the person's soul - their memories, their essence, and anything else that comes with a soul. So, unless the person died in a device as advanced or even more advanced than the Soul Translator, I highly doubt that you can make anything more than a digital ghost that has some characteristics of the person (see Griselda's and Sachi's "ghosts"), and even that was accomplished only because the Cardinal System just happened to decide to store specific data about the players because they felt unusual to it, rather than the FullDive machine having some data saved.
Still, if you have sufficient amount of "event" data, a brain like structure, even if virtual, could possibly fill in the missing parts. Current research on human brains and memory shows that most of us don't remember as much detail as we thought and that the brain is capable of "filling in the blanks" to give the impression of a detailed and vivid recollection.
The idea of "essence" is philosophically suspect anyway. Who's to say that the step between Yui and a fluctlight is really that far? It is a fictional world after all.