Nope. My friend studied in England for five months, and her boyfriend waited for her. I don't think him leaving means he's letting go of her as his girl. I mean, when people in the military go off, it doesn't automatically mean their counterparts are available, be they married or not. When people go to study abroad or across the country, they don't necessarily cut their relationship off the moment they walk out the door. Many stay true and come back to each other. So, I really don't think the simple act of him saying goodbye constitutes a breakup.
Though, if we were to analyze this from the point of view of the other men of CSI, she already IS fair game, thus their approaches to her would not vary in Grissom's absence. So, since they've all be fairly hands off in the last few years, they would probably continue to be hands-off and would not be emboldened by Grissom's absence since, to them, it means nothing special in regards to Sara.
So, to those who know, Grissom leaving does not make Sara fair game. To those who have no clue, nothing changes.