Saruman and betrayal

[Kuruharan]

if you could catch Saruman by surprise the way the Ents did and get it over with quick. A siege certainly isn't an option in my mind, because you can't spare the troops and time for a siege with Sauron sitting across the Anduin.

Hmmm...I think it might depend on when Saruman's treachery was discovered.

Say, for example, that somehow Saruman was exposed years before Sauron wanted to move. Would Sauron attempt to rescue Saruman?