One of the trio's biggest errors?: Not awaking Snape in the shack (PoA)
Once Pettigrew had been resumed to human form, what if the trio DID decide to awake Snape?
Snape sees Pettigrew - sees Sirius is innocent. When the Dementors attack - Snape casts a patronus. No time travel needed - Snape tells Fudge what really happened - Sirius is cleared and doesn't have to live as a fugitive.
Just a chain of events I'm wondering about. Thoughts?
EDIT:
Hillariously, I think Snape would help clear Sirius's name but still advocate for the trip being suspended for being out of bounds at night.
Snape's plan for the night would be:
"Alright lets clear Black's name... Then we'll get you suspended Potter."