I think the only objective of Vidur is to hide the truth of the scandal. Till the time Prem was in Rishikesh not willing to return, Vidur had no fear of exposure of that scandal so he didn't tell the whereabouts to DB
But now that the truth is being filtered he is stopping it
I think the mastermind (whoever he is) had made a offer to Prem via Vidur that Prem let his wrong activities carry on and turn a blind eye to it. Prem definitely knew some wrong practices of Mahajans that's why he said Mahajans nhi badle hain to Vidur.
Prem was probably threatened that if he does whatever mastermind says he will be cleared of the scandal if not then his family could be killed... So Prem decided to leave.
Vidur still offered Prem to return with same conditions which Prem denied and feared that now Mahajans will know his whereabouts but Vidur isn't evil, he is just loyal to mastermind and doesn't want him to be exposed. So he decided to leave Prem as he is until obviously Bhumi called him..





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