Sorry to hear of your diagnosis, but please follow your doctors advice, they have studied for years and have probably seen many cases like yours and so are advising you from experience, it may be hard to accept but i'm sure they can advise other less stress inducing activities to replace running.
We only get one shot at life and should also look to minimise risk where we can!
Well said Screama, we all make choices in life and those choices either improve or negate any work life balance we strive for.
in regards of charity places , I'm with the majority and this extends to all race entries, if you want the entry bad enough you'll do whatever it takes to bag that entry, if that's gaining a GFA time, sucking it up and raising the cash for a charity place, or waiting until the odds work in your favour and you gain a place in the ballot.
For me the charity runners and the elites are the focus of the London marathon and especially without the charity runners london would not have the same appeal.