It think that they are basically asking "If this is not the truth, then what is?" "What will I use to fill that place in my thoughts that were occupied by the WTBTS teachings, since i have been taught that every other belief is false"
And that is a fair question to ask coming from a person who's entire belief system is teetering on the edge.
A person does not have to know what is right to know when something is wrong. Does a battered woman have to know where she is going to sleep tonight to know she is being beaten now?
Does a person in a burning house not leave the house because they do not know where they will sleep tonight?
To me, it does not have to be a instantaneous exchange from one belief to another. You find out what you currently believe is wrong and get out,.. then start to slowly look for what is right.
NJY aka Scummydross