Usually quest items can be reobtain by talking to an NPC - after deleting them. With Fallen God's Ring it seems not to be the case.
It was reobtainable from an NPC at Port Ratt which is gone.
Talking to Basquean Ljurik or Merio doensn't give the option either.
Do I have to quest all up to Star's End again to obtain it?
You should be able to get the item from this NPC in exchange for 30 energy https://bdocodex.com/us/npc/58014/
NPC doesn't offer missing items anymore.
Have you checked the prerequisites for the exchange in the link I gave you?