It would have made no impact even if a newcomer was cast in the role. Mohra was largely a male centric action film with Raveena’s role limited to one scene before a song and one scene after the song. The reason why she got popularity after the role was because of the two songs- “Tu Cheez Badi hai Mast Mast” and “Tip Tip Barsa Paani”. Yes, one thing that worked in favour of Raveena was that she was a better dancer than Divya, and did absolute justice to the songs and her dance is one of the highlights of the film. Also her chemistry with Akshay Kumar was really good (they started an affair at that point)
After having good screen time in the first time she doesn't have anything to do in the second half as such as action takes centrestage. So like Vishwatma which was also directed by Rajiv Rai, where Divya Bharti was largely remembered only for Saat Smaundar song, had Divya been a part of the film she would have been remembered only for the songs.
Mohra became a massive hit because it was made stylishly, action was brilliant, script was tight and Sunil Shetty and Naseer acted pretty well (Sunil Shetty had a better role than Akshay in my opinion), and the music was chartbuster. Rajiv Rai has delivered hits like Tridev, Vishwatma and Mohra with actresses who were not that big a star at the time of making. So Divya Bharti or Raveena wouldn't have made much of a difference.