Ok so my theory is Vansh made Riidhu his POA in his absence, hence Riddhu there..
Riddhu will try to fill Vansh’s responsibilities
Every one will hate her but she will give damn.
She will try to find Uma’s murderer & will try to take revenge from Kabir
Kabir arrested him knowing Ragini was alive.
AP-K won’t be able to property 
They will find Vansh disguised as someone else.. they will test him & figure he is someone else & not Vansh
& bring him back to get Riddhu out of VR mansion
Ekdum Ektamaiya style.. (I have watched too many ITV shows 7-10 yrs ago)