I don't understand why exactly Baa Bapuji left. Vanraj has time and again assured and proved that he treats them like Bhagwan and take care of them. Building a tower and having a separate space for each other is a good idea for a family that is as incompatible as this. Sometimes a little distance brings people closer as they can do their own thing. In fact Vanraj also made arrangements to keep them close just separate flats, so that in times of need they can be nearby. I think he also mentioned that the house is old and needs regular maintenance so it may not be economically feasible to keep the white elephant.
Isme itna nautanki karne ka kya hai ... Aisa bhi nahi hai ki koi bohot khuobsoorat memories banayi hain sabne Shah House mein ki use rakhna bohot zaroori hai. I understand that Anupamaa and Bapuji might have memories of Tosu, Pakhi and Samar doing potty here and there and Maa cleaning it up, while Vanraj screaming about having his tiffin box, Baa asking for her breakfast. Baa throwing all the vegetables on the floor and Anupamaa picking them up. While after Maa finishing all the work Bapuji reprimanding Baa not to overload his daughter. Baa insulting Maa at different corners of the house. But these memories they can always recreate in the new house. 