Yeah without playing the "good ending" of the investigation storyline you can't become CEO. Only way to get that is recording Cassidy, so loading a save before it happens is the only option...
The office harem is for me probably the best part of the game so far, but it's of course up to you if you want to replay that part or not.
Those are the conditions to trigger the event:
As I said after checking your save on the previous page the disappearing of Lexi worked fine for me. The event of her actual disappearance happens (there's no visual feedback, she's just gone after this) once I change the area after loading the save. After waiting one week and till next Friday 17:00 (or Saturday 17:00) the event triggers to search for her. Do you use any unofficial mods?
No clue about Kylie, if she's already in prison you should have already some cam footage about her (and brought it to Camila), otherwise she wouldn't be in prison...