Zeev Schiff says that the IDF would in fact leave Gaza after the removal of the settlements, but that they would return to respond to rocket fire etc. It's not clear whether the IDF would cease to man the border with Egypt, and there are lots of problems regarding how Gaza could possibly be self-sufficient. It's also likely that the anticipation of evacuation will lead to increased terrorism, so as to create the impression of "exit under fire".

Schiff thinks that Sharon should have done this when Abu Mazen was first installed. Though I would note that if he had done so it would not have been construed as a "unilateral move", but rather as one of those pointless "confidence-building measures".

The media today has a lot of discussion about how the Gaza settlements would be totally levelled when they are abandoned. MK Ahmed Tibi called for them to be left behind for occupation by Palestinians in refugee camps - but this is simply posturing, as the Palestinians have long opposed any attempts to improve conditions of the "refugees" to the extent that they might be willing to stay where they are.