Denise Crosby has great talent as a villain. Just look at how she jumped off the screen as Sela. After seeing where the writers went with Ro Laren, I feel confident that Yar would have filled that role. She would have been a friendly foil, either as a member of the Maquis to set up Deep Space Nine, or as an onboard intelligence officer like Malcolm Reed in Enterprise.
In the early seasons — while Roddenberry’s edict that the crew not have conflict was in effect — I think she would have befriended Data and Geordi, and would have been in many scenes with them.