I've been assuming that the real Mandar will come back. As for him staying away on purpose - this is where things get fuzzy because if he was still alive - did Raghav know about it and is purposely keeping this information from Pallavi so he can keep her with him? Or did he put the responsibility of Mandaar's care to that lady he spoke to, and she let Mandaar go but never notified Raghav? Right now it seems like even Raghav thinks Mandaar is dead, so did Raghav not stick around at the hospital to see what happened to Mandaar?
My only other theory is Mandaar lost his memory and thats why he was never able to come back. Raghav is keeping it all a secret because he's too scared of losing Pallavi - but to be honest this seems too cruel for Raghav yet at the same time, he's so desperate to keep his family (which includes Pallavi) he maybe would do this? Or Raghav did drop him off at the hospital and just never followed up with him and assumed he died ? Idk, that seems less logical to me. Who brings a hit and run victim to the hospital and not at least wait to hear the news?