Yes now I believe for certain the possibility of Michael not being by the Don's side until while being in Sicily because of you two now reminded me that before the assassination attempt Michael was being distanced from his father not only from the life style point of view but also as a son caused by their disagreements on the career path. So it wouldn't really make sense if he changed his life style path right there in the hospital room with him because logically you'd have to start out with being a son first which wasn't the case until then.
Regarding the flashback scene, I was always interpreting it as if Vito and Tom were planning a legitimate future for Michael, distanced from the family business and that he even didn't want that but wanted to simply do it all by himself without his family pulling any strings.
