One of the great and subtle arts of Congressional committees is who NOT to get testimony from, and what questions not to ask. The best way to avoid really damaging information, especially if knowing it would demand some form of unpalatable ACTION, is to make sure it doesn’t appear in the official record.
In any case, I would bet that Hastert won’t be actually testifying anytime soon. Of course, I could be wrong – so I won’t actually bet.