The point of the Valerie Plame affair is that telling people she was a CIA agent is a high crime and misdemenour as defined by the constitution. That term was designed to be about acts of treason or sedition, which is what outing a CIA agent basically is. All this came out in the Clinton impeachment in which lawyers argued that the original framers of the constitution intended it to mean crimes against the state only.
If Rove did this then he may be going to jail for 10 years unless pardoned. It's quite possible Bush and Cheney knew about this and so as co conspirators they would fit precisely into the constitutional definiton for impeachment the way it was intended to work. If they weren't above the law and they did this, then they would be going to jail too.
There aren't any more tape recorders in the White House to prove it though. Wilson has in effect accused Bush and Cheny of truly impeachable offenses.