Willow Rosenberg, a beloved character from Buffy the Vampire Slayer, almost had a different actor portraying her, and this wasn't the first time something like that had happened. It's difficult to imagine anyone other than Alyson Hannigan playing Buffy's loyal friend, who goes from a quiet companion to a powerful witch. However, in the unaired pilot, the role of Willow was originally taken on by Riff Reagan, but it didn't pan out, and Hannigan quickly made the character her own.
In a recent interview with Shut Up Evan: The Newsletter, conducted prior to the SAG-AFTRA strike, Melanie Lynskey, known for her role in Yellowjackets, revealed that she initially declined the opportunity to audition for the role of Willow in Buffy the Vampire Slayer. Lynskey explains that this was partially due to a visa issue, but mainly because her agent advised her against working in television. After eventually deciding to audition, the role went to Hannigan. Lynskey also speaks highly of Hannigan in the following quote.
“I don't recall if it was an official offer or if it was more like, 'Would you be interested in auditioning?' or something similar, but we stayed in contact afterwards. Eventually, they were looking to replace the person from the pilot, and I had kept in touch with [Joss], who asked me, 'Do you now think you'd like to give it a try?' Having watched the pilot and thinking it was great, I discussed it with my agent. However, it then turned into a situation where I had to go through an audition process. So, I auditioned... Alyson Hannigan ended up getting the role, and she was absolutely amazing. Everything turned out as it should have."
Other Alternate Castings in Buffy the Vampire Slayer
The iconic titular character of Buffy had several well-known alternate casting possibilities. Ultimately, Sarah Michelle Gellar was chosen for the role, but other notable names considered for the protagonist included Katie Holmes and Selma Blair. Interestingly, Charisma Carpenter, who later portrayed Cordelia Chase on the show, also auditioned multiple times for the role of Buffy. Conversely, Gellar originally tried out for Cordelia.
Other key characters also underwent similar casting decisions. For instance, Bianca Lawson, who would later portray the slayer Kendra in season 2, could have played Cordelia. However, Lawson revealed that she had already committed to another project at that time and couldn't take on the role. Nathan Fillion, who later appeared as Caleb in Buffy season 7 and collaborated with Whedon on Firefly and Dr. Horrible's Sing-Along Blog, was a potential choice for the role of Angel.
In a potentially significant deviation, Ryan Reynolds was considered for the role of Xander Harris in Buffy the Vampire Slayer. However, this possibility didn't progress as Reynolds, who would later become famous for his portrayal of Deadpool, declined due to his reluctance to be part of a high school show. Consequently, breakout soap star and Emmy winner Gellar became the most prominent name associated with the WB series. Although the other actors in the ensemble cast were relatively unknown, they quickly formed one of the most adored groups of friends in the entire teen drama genre.
Source: Shut Up Evan: The Newsletter