Sync mode is about providing a guarantee that the data exists on more than one server *before* we tell the client it's committed. If you don't need that guarantee, you shouldn't be using sync mode. If you do need it, it's not clear to me why you'd suddenly not need it the moment the going actually gets tough.
As I understand it what is being suggested is that if a subscriber or target goes down, then the master will just sit there and wait. When I read that, I read that the master will no longer process write transactions. If I am wrong in that understanding then cool. If I am not then that is a serious problem with a production scenario. There is an expectation that a master will continue to function if the target is down, synchronous or not.
My expectation is that the master stops writing checks when it finds it can no longer cash them.
