I certainly wouldnt walk the event with walking sticks etc personally. The key thing (for me ) is not doing yourself any long term harm.
Lots of people pull out of marathons near the event and many of these have raised tons for charity - have a discussion with your charity an d(if you are unfit) see if they can suggest an alternative marathon for you to do later in the year / next year.
Agree you could do entirely what Madbee says and it would be ok probably.
But if it were me and I was focusing on a big prize (sub 4) I would retain focus on that. Will be plenty of opportunity to run fast 10kms after the 2nd November. It will be hard (I guess although some people manage) to time a 2 hour run finishing at teh 10km start time - the gap wouldnt really work for me.
We all book and then miss races - its an occupational hazzard.
The Expo is slightly bigger than London. It also has alongside it a series of seminars. Worth going to a few . I heard an amazing talk from the Hoyts and also got a lot of info about the race itself at another from the Race Director.
There is a 5km run (think its moved to the Saturday now) which did finish at the same place and was worth doing as a leg loosener after the flight as long as you dont get carried away.