You would think that they should be locked to your account like a Bonded pet, but then they do not run away on their own, and usually vanish by accident or neglect. So I guess personal responsibility is key here, and I am guilty of soulstone loss myself. I feel your pain on this issue!!
It would be nice to see a lost and found for soulstones created by mythic. Some way for players to drop them in a box in say Luna, and when a player double clicks that box, it auto searches for any valid soulstones for that account. It can't be that hard to code right?? I have to believe that the majority of players are honorable and wish to find homes for lost soulstones. We all know how hard it is to raise skill, well some skills, errr well maybe how hard it used to be!! Regardless if the skills on them, I'd pay handsome to get my two stones back again!!