The Colts are going to have to either completely retool their offense or hope to God that Collins suddenly learns how to do things he's never done before. Manning gets a couple of plays called into him, scans the defense without a huddle, and then calls out the play on the fly. Collins isn't going to know the playbook well enough to do that. Also, the Colts offense is deceptively simple. It's largely just your basic routes being run, but the high degree of precision achieved through all the practices with the QB and receivers makes it difficult to defend. Collins won't have that level of rapport with that group.
To make things worse, the bye week doesn't come until week 12 for the Colts. Starting games
Texans
Browns
Steelers
Buccaneers
Chiefs
Bengals
It's possible that the Colts could be 0-5 heading into Cincinnati.