As I understand, having a security clearance means that you have to submit to a polygraph at any time. If he refuses to take the polygraph, no big deal, it just means that he can't be ranking member on the committee. Look for him to step down from that role in the committee.
Tend to agree. I doubt if they will ask him to take a polygraph. But if they require his staff to take one, chances are they will spill their guts if they know the truth of the matter -- especially if they were involved. Plea bargain for testimony, betcha.