Yes, I agree. Even before they released the casts, I knew that most of them are going to be gone as they entered different universities. I am open to these new characters. I do believe or think that at least MoRaoYuLok will make an appearance as their reunion?? maybe Tarn as well? idk haha but there's a possibility.
I think Hoon and Teh's Ma are going to be there. I think they still play a big part especially Hoon when the time comes that Teh will tell his mother about him and Oh Aew. (I think if it has a scene like that, Hoon will be there)
Overall, I understand why and it's okay for me. I will just imagine in my mind that they all got their own happy ending especially Bas and Tarn.
However, during the Offering Ceremony of Part 1, if I am not mistaken Hoon and Teh's Mother were not there but they played a big role on ITSAY 1 so there's still a chance for the old casts haha.