I don't know about whether a soul crystal can function if it fragments, but if you want to play up the quasi-sentient bit you could always have it conveniently fall off of his person One Ring style.
V'aleera's Wiki - https://wiki.ffxiv-roleplayers.com/pages...eera_Lhuil
V'aleera's Tumblr - valeeralhuil.tumblr.com
V'aleera's Tumblr - valeeralhuil.tumblr.com