what do this quote mean that Demise be a formal affair?
I don't know what "Demise" refers to. A formal affair is a party or occasion at which long dresses are worn by women and tuxedos are worn by men.
demise means death, how do death be like a party?
Ohhh! I see now.
I think it means that death is a solemn occasion and deserves a formal ritual.