Oh I agree this is a matter of internal labour politics, but he squeaked in with 70% of the PLP voting yes and virtually all of the big beasts so its a comfortable squeak.
If he has notice of a lot of senior MPs like Straw and Prescott voting against he has choices.
Go ahead anyway and force them to resign from the cabinet and bull his way through - it means a major split but if he feels strongly enough about it the labour opposition's option is to vote him out as leader or support a Tory no confidence vote on another issue with all the consequences at the next election that will bring, or live with it.
Go to the country and ask for a war vote, not really credible as, presumably, the opposition within labour would be effectively campaigning against him.
Pull the vote and do nothing.
Form a national government of Blairites and Tories for a while and fight over who is the labour party.
I suspect the tactical best answer with hindsight for Blair would be to bull it through and call an election, either national or labour leadership the day after Bagdhad falls. If people want to oppose him while all the news is of Iraqi's celebrating the overthrow of Saddam good luck.
The real game changer would be if Brown et al came out against but thats really a Brownite coup not necessarily a move against the war and has electoral consequences all of its own.