That’s difficult to say. Mulder’s character hinges on that night, revolving heavily around the quest for “the truth” in order to make sense of Samantha’s abduction. He worked himself to the bone to get top marks, graduating with exemplary scores both as an undergrad in Oxford and a student in the Academy to keep himself busy in order to ease those memories. He went into law because he wanted to find Samantha and to uncover the true story behind her disappearance. As The X-Files states, his relentless drive and successes have all, in great sense, came to be as a result of Samantha’s abduction.
Take that night away, and what do we have? Who knows. This is, like, ground-zero. However, I like to believe that Fox Mulder would have always been a hard-worker, a man who makes goals and commits to them. I feel like he’ll always be true to himself and believe in himself. Always want the truth. Always want the best. Always lawful and good. I think he would have worked in something related to space had it not been for his trauma–most likely in NASA. He expressed a deep love and interest in the space program in season one and was also seen dressing up as Spock! Pretty much puts on display his liking for sci-fi. Science, primarily that of the cosmos and life beyond, appears to be a constant no matter what universe Fox is in. And, because it feels so strongly Mulder, I think he’d also still believe in extraterrestrial life, at least find the idea completely plausible, if not irrefutable, that there is life somewhere out there beyond Earth. I don’t feel he’d be the conspiracy theorist or as ridiculed, either, and though still someone who’d rather keep to himself, no less lives a different, normal life, one he’ll probably never have canonically.