Guys am new to the forum and just went by this post and I feel it will not be appropriate to cast the same person as Parvati since Parvati is completely different to Sati and it has to be a new person to play the role. I guess everyone is used to Mouni as Sati and since she and Mohit make a great pair one tends to get emotional and want to see the pairing again.
Lets not forget it is a mythological series and not a typical daily soap. The story cannot be modified to people's whims and fancies and neither the characters retained due to audience preference. It is the story of Mahadev and many aspects will be covered so lets be positive and accept the changes am sure it will be a treat to watch in the coming days.
I am not here to hurt sentiments because even I like Mouni Roy but one has to think logically. Anyways lets hope for the best.