I don't think he could of actually, I mean one of the biggest incidents in the Buffyverse was the Angel changing over to Angelus storyline, and it effected the course of the show so much and it would not have had the same impact if he was not in a relationship with Buffy, I mean lets face it we are not nice people we like to see our heroes be pushed fully to their limits, we want to see them go through hell and back, and we want to see them suffer from love and loss, that's what make's Buffy so great it is not afraid to touch on the big subjects.
Having Buffy fall in Love, complete and utter head over heals love, is a big storyline, That allot of other shows would cover, but then have the lover of the hero turn evil after she sleeps with him for the first time, not just their first time but her first time ever, then have the lover torment her friends, and murder the people around her, before resulting in a fight to the death in which she has to kill him, just so the world can continue for another day! That's freaking huge, and it was covered in one season!
I mean I think if Angel had not had this love storyline with Buffy, he would have been pushed to the back, and Angel it to big a story to have pushed to the back, I mean that's why he got his own show, I just don't think it would have been possible to continue that character in the way he was heading in season 1.