An interesting question, brought up by the vote at the Labour Party conference last week. The conference delegates were faced with a choice between two motions - one demanding that a date be set for the withdrawal of British forces from Iraq, and one stating that British forces should "be withdrawn if the Iraqi government requests it". Obviously, the second option would have been seen very differently had it been put as follows - "that British forces should remain in Iraq indefinitely, unless the Iraqi government requests they leave", which your keen & agile minds will perceive as being much the same thing. I would strongly disagree with the "anti-war platform" for reasons of practicality, as I don't think that setting a date for withdrawal would be a good idea at all. You could call it the Kerry Problem ("How can you ask a man to be the last man to die for a mistake?"), which is that the intervening period will unavoidably be a grim and pointless struggle continuing until the last Warrior containing the last soldier drives over the border into Kuwait. Not only that, but the act of setting a date for departure forfeits any bargaining strength we may have, both in Iraq and with our gallant allies. This may be described as the Indian problem - once the decision to bring forward Indian independence was taken, partition could no longer be avoided as both parties knew that they could attain their minimal goals by waiting it out until the trumpet sounded.
Also, it is probable that the other side would intensify their efforts in the run-up to departure. Being the hard core who chased the British into the ships would count for plenty in the struggle for power afterwards. This might be called the South Lebanon problem. The Israeli army's withdrawal from Lebanon in 2000 was rendered much more bloody by this factor. There is also the issue of those groups in Basra who have so far been supportive. Will we have to take them with us? Or will they change sides, or simply be slaughtered? (All of these happened in South Lebanon.) What happens then? I still, faced with the option, would have voted for setting a date, as it was an opportunity to force accounting for the whole vicious disaster. (Dump the principle but stall the implementation...)
The problem is that absolutely no good option presents itself. Continued occupation? More death, and more aggravation, more waste, and probably more problems as yet unexploded. The provinces in the MND(SE) zone have recently been granting themselves susbstantial autonomy from Baghdad - will a oil-rich "Southern League" emerge? (Now that would be a classic case of short-term relief being long-term poison.) A timetable for unilateral withdrawal? Reasons above, plus the possibility of a "Southern League"/Shia rebel zone erupting between Baghdad and Kuwait. What else? UN peacekeepers? Who will provide them? Will they be effective? What will they do? What if they fail? This doesn't even take into consideration the possibility of either a post-election US offensive in al-Anbar and Baghdad, with the predictable Shia explosion, or a US scuttle.
(Careful readers will note a certain symmetry between Tony Blair's problems after the announcement of a date for withdrawal from No. 10 Downing Street and the hypothetical ones of his army in a similar case.)