This made them bankrupt, they had to sell colleges and airplanes as the membership desolved into many groups.
007 - it depends what the funding structure was of this church - for example if it was tithing, then yes a significant drop in membership would be a problem.
Correct me if I'm wrong but my guess is that the WTS finances are not dependent at all on the membership. As has been stated before IMHO the JW religion is potentially a loss-leading front for the main business of financial instruments and property. So the core drivers of revenue are not the membership any more.
Add to that the downsizing at Bethel, the move to upstate, the sell off in Brooklyn and you have an org that is following some sort of strategy here - these are not random events.