I suppose it's moot at this point, but I was surprised when Bush on 3/17 DIDN'T say that the assault takes place in the absence of disarmament, regardless of whether Saddam stays or leaves. Prior to 3/17, I heard Powell and one other official state that very clearly.

So the news you heard may be from a Bush quote that preceded 3/17.

The point is interesting in a legal or philospohical sense, as it directly relates to the motivation and justification for military intervention. On the surface, it could be interpreted as "I don't give a crap about the weapons, I want regime change." However, Saddam simply leaving certainly leaves questions about who's in charge the next day. What if Saddam should leave, with a civil war as the immediate result?