I think they will replace their beliefs as they have many times in the past and they will have a certain amount of membership churn as a result but most "believers" will simply switch what they believe to the new truth as they often do.
The reality is that most JWs don't really knowwhat they are supposed to believe and don't really believe the things anyway which is why switching when they are told isn't so disruptive as we imagine it should be.
It's increasingly a lifestyle religion and social club so as long as they keep things 'easy' they will continue. The people who don't like the new beliefs will be replaced with new members who find the new beliefs appealing.
The days of hardcore JWs in it for the biblical analysis and search for truth are long gone. There are probably a few scattered atround but now it's all about media, presentation and slick delivery and above all else - profitability ... branches and congs that are too difficult are closed down.