Thanks for the tag!
You know I'm not sure if Raghav has a legal plan yet.
Although he's smart, he's the kind of person that likes to compartmentalize issues. Deal with one thing at a time. I think that's why he said "let's wait for the DNA test". Now, that could also be because he's going to build a legal case/ get lawyer's advice in the mean time. It could go either way honestly. Do I think he's definitely going to get a lawyer to resolve the issue quickly, yeah no doubt.
He's definitely detected Mandar's intentions/desire to have Pallavi already. This was his worst fear anyway so I think he's mentally prepared and knows that there will be a legalities to deal with eventually. I just don't know if he's coming up with this masterful scheme of thwarting Mandar lol. I think he's too focused on building a relationship with Pallavi to really care at the moment. I think he needs to be in a position dealing with the legalities for him to come up with a plan to resolve the issue. (i.e. He'll get triggered with Mandar walks in with DNA results saying he's Mandar).
I think both scenarios you discussed could happen - Raghav reveals something unexpected to "win" and Pallavi standing her own ground and refusing to go back to Mandar and filing for divorce from him.