Help! Emergency Marathon Strategy Needed

I'm desperately in need of some advice ahead of Brighton Mara this Sunday.
My training has been seriously compromised by a couple of 3 week long spells with calf pain that wouldn't allow me to run. I've got to this stage of hanging on to actually starting the marathon with four sessions of massage, daily exercises, stretches and icing and my legs are now in the best shape they've been for months. However I am seriously undertrained, I feel as if I've completely lost strength, stamina and speed. Never got my long-long runs done properly (managed 4x13, 1x16 and 1x18) and last few medium length runs have only been completed with walking breaks. Haven't done any interval/speed/hill work for months as it was that which kicked off the calf problems. SO...
How do i best approach Sunday? I am considering walking for a minute every couple of miles. Is there any science at all I can apply to dramatically rethinking how I survive - and yes, my only goal is survival. Has anyone else found themselves in a similar situation and triumphed?

Two options...

Go very very slowly ... be prepared for a long walk.

OR

Call it a day and train properly next time.

Start very slowly and be prepared to DNF if the calf problems come back? The ability to "just get round" on little training depends on your base fitness I guess.

Can you defer your entry to 2012? Unless you carried it over. If you not at all confident and
do not want to risk the injury recurring. Might be best to defer. At least you have time to rebuild
yourself back properly.

Running a marathon especially recovering from injury is a dodgy one. You haven't trained
for 3 weeks. Fitness-wise you should be ok. But its the calf. You might feel its in the best
shape, but you can run Brighton and that injury could reappear. Even if you run/walk.

Unless you done any running since recovery will depend how your legs feel. If it feels ok,
then you could run/walk the marathon and see as you go along. If the legs feel tired or
abit heavy, then think what 26.2 miles will be doing.

Its your body, your decision. But best of luck whatever you do.

Deferring sucks but it is the sensible thing to do in these circumstances.

Otherwise, you need to plan a walk-run strategy. If that's the way you've been forced to train then there's no point planning to run your way around 26 miles. 

I would defer, I did a mara in 2008 that I hadn't been able to train properly for and it was crap.  No achievement, a shit day and felt crap for weeks afterwards.

If you've planned a run walk strategy all along, fine, but be honest what's the point of doing the race if you can't do it well by your own standards?

Thanks for the responses. It may be unwise but I'm going to give it a go anyway. I'd rather not finnish than not start. My strategy is going to be running 2 minutes slower than I'd planned and hang out at the back.

Woop woop. Made it. And pain free too.