Hey, bro. From what I read, Albert Park has an ongoing agreement to host the Australian GP until 2023. Read it from this article.
Yeah, I haven't heard any rumours about Melbourne giving up a GP race. It has already invested a lot of time, goodwill, and fanbase -- not to mention finances -- to host the first race of the season every year. They are proud of the heritage and the prestige of being the home of F1 -- and a bunch of other sports event like the Australia Open tennis, Melbourne Cup (horseracing), rugby and cricket finals, etc. This I can say: It may be the final Melbourne GP I'll go to. Will try to experience other circuits in the future, hopefully Japan or US.