I am hugely intruiged about the geographic spread of you lot. These runs sound like a real hoot but I am puzzled, given the horror stories about rail and bikes, how you all manage to get home (notwithstanding chips, beer, wine etc) and the level of confidence you express in not being stranded miles away. Those of you that do a couple of hundred miles on your fixie up ben nevis before going to work work I can understand, but we lesser mortals......
All good questions.
Firstly, you need to have a certain level of confidence in your bike. For example, as part of the FNRttC initiation ceremony, you're required to confirm you've read the FAQ, and
this neatly summarises the key things to go over before hand. Generally on rides you'll usually have a number of people who carry enough tools for minor repairs. Granted, if a wheel goes completely, then you're stuck. On this sort of ride at night, there's a lot of open countryside so getting back to civilisation could mean a long wait. However, the chances of that arising are very, very slim.
Train-wise for the journey back, it's not normally an issue. It's been very rare when a rail official has stuck to the rules and limited the number of bikes allowed on, and normally that's only on the 1 or 2 car units. For something like this, some may cycle back, or it's just over 20 miles to Ipswich where the trains have good old fashioned guards vans capable of holding 20+ bikes. If there's engineering works, then you can always cycle to the next usable station! Although before starting this, in any event I'd checked to make sure there weren't any planned works on the line.
...but you'll be hallucinating superbly by then so it's ok. 
That was pretty slow. I 
