Im not sure half the courses will disappear. Melbourne's problem is not too many courses, it is too many courses in the same part of town. If they were more evenly spread like Sydney, or indeed just about every other city in Australia then it would not be so dire.
I just did a quick google earth check, and there seems to be 19 courses within a 10km radius of Royal Melbourne. That is competitive death for those in the bottom half of that list, or at least the private ones.
So yes , there are too many in that SE region, but closing is actually a hard thing to do. At least I guess most of them own their land so the option is at lest on the table, but one issue is what to do with the money. All of those clubs in trouble are not for profit, and a requirement of that is that their constitutions forbid any proceeds from sale of the land being distributed to the members. Yes I suppose they can always change their constitutions and distribute the cash amongst members, but then it all becomes taxable.
The other problem is one of, who would actually buy the land?? Yes there are different councils, but I suspect the issues at Dingley would scare a lot of developers off. At the very least the price would be severely reduced, such that I suspect if you did the sums and divided the greatly reduced value by the number of members, then subtracted tax, there might be just enough left, if you are lucky, to pay the joining fee at a 2nd tier sand belt club.