this is less of a prediction and more of wishful thinking filled to the brim with misplaced optimism and copium.

i hope that the Ruin DLC follows the Afton ending(ik that Burntrap's probably actually Mimic not William but shh), but its a bad ending. Cassy spends the whole game running around the PizzaPlex looking for/talking to Gregory, but never finds him. Until she gets to Roxy Raceway, where she finds his body. We get a cutscene where she looks at Glamrock Freddy and he's got those Fnaf 1 possession eyes, and Gregory say 'Hi' through him.
This would kick off a new era/story line for Fnaf, where the whole old cast(William, Michael, Elisabeth/Circus Baby, Cassidy, Henry, Charlotte/Puppet, etc) are all dead and Vanny/Glitchtrap and/or Mimic replace William's role, Cassy(or someone else idk) replaces Mike, and Gregory and GR Freddy replace Charlotte and Puppet. And maybe they could even tie the books in a little more by having the new cast meet the Charlie robot from the books. idk.

tl;dr, steelwool will use ruin to fix/change/do anything to the plot. there is a 99.99% chance they will not.