For now I'm gone - self-explanatory
BUt never forgotten - It's probably more literal than this, but this line makes me want to think it's in Memoria.
Once used for protection - also self-explanatory
But no longer so - taken control of, maybe?
I am never seen while im alive - was once living; implies that it is undead or created somehow
But I still move but with help from my master. - further pushes in the direction of undead or machine.
The problem is, I don't know about any significant undead in the game other than Soulcage, but he doesn't seem to fit the second or the last line. (is it Soulcage?)
I'm probably way off on the second line, but that's the kind of thing I would use in one of my riddles, so it's just how I think.