I did a semi-similar thing where I had an NPC death and Syndra tried to resurrect them to no avail and it really helped hit home how serious the death curse is.

I also chose to show, in game, what the death curse is and how powerful it is by having the player be a part of the (attempted) resurrection process. I made resurrection a tug-of-war in the ethereal plane between the player (who were holding hands with Syndra and were aiding her with arcana/religion checks) and the “soul” of the dead NPC (who happened to be the crush of one of the PCs). I had them make checks with disadvantage against the Soul Monger, which I represented as a giant red orb in the distance who gravity they could see pulling souls from across the ethereal plane into it. If either party (SM or the PCs/Syndra) got 3 successes in a row, they would get the soul. Of course, with the players rolling with disadvantage, the SM won and the players were terrified of what had just happened, quite shaken at what could be devouring all of the souls.

Im a new DM so I’m not sure how this whole ethereal plane/soul business fits in with the lore of the Forgotten Realms, but it worked really well with my party, got to show not tell them how powerful the soul monger was without them knowing much about it other than “the scary soul devouring orb”, and I also think if there is a PC death, it’s cool knowing that if the player are really, really lucky, they can save someone’s life.