(This fanfic happens At the end of security breach)
After the blob had captured william, it started torturing william for all the pain that william caused the souls in it, then, the blob realized how william comes back, his remnant, if they removed william's remnant, william soul would pass on, so they did that, they used some custom-made syringe to remove william's remnant. Cassidy decided not to put william's soul in UCN again, because that would give him a chance to come back, William then woke up in hell, he said:
-WHAT!? WHERE AM I?
Oh, you're FINALLY Here! - Said a misterious figure, William then realized, it was the devil, and he was in hell
William said:
-NO! I ALWAYS COME BACK, DON'T I?
Not this time - Said the devil, then the devil started doing william's punishment, he made a punishment very similar to UCN, except there was no way for william to come back, especially not after the blob destroyed his remnant.
This was the true end of william afton, this time, he wouldn't come back.