First and foremost, as per me moving on doesn't really have to be only when you have someone else in your life. To me it just means putting yourself and you happiness above the one who is not in your life anymore.
As far as what we have seen about Pakhi till date, even if Samrat was around, I don't think she would have genuinely given their marriage a chance. Hell, that woman married Samrat to be close to his brother.
I believe moving on would have been more easier for Virat in that scenario because he would not have the guilt of seeing her lonely. Also, someone with Virat's morals would have maintained his distance with Samrat around and eventually he would have moved on.
If he was married to Sai with Samrat around, he would have maybe realized his feelings for Sai earlier with no Pakhi trying to guilt trip him and it would also have been easy for Sai to lower her walls since Pakhi would be not be so open about her affection to Virat.