A Different Phoebe
It’s really hard to imagine any of the characters portrayed by any actors apart from the ones that made them iconic. Could you imagine anyone but Lisa Kudrow playing Phoebe? However, Ellen DeGeneres was actually considered for the role! Things would have been quite different, but Ellen turned down the role, leaving it open for Lisa Kudrow to take.
No Monica For Chandler
Once again, it’s difficult to imagine a Friends storyline in which Chandler and Monica don’t end up together, since they seem perfect for one another. However, the show’s creators actually considered making Chandler gay. Maybe this is why there are so many references to other characters thinking that he was gay when they first met him.