I don't like the idea of naming an official "contingency" server and I'll try and explain why.
I think we'd risk confusing people who "glance" rather than read the website into thinking we're rolling on a different server and that could cost them money to fix. At the first possible moment that we can confirm our "home" server, I want to shout it from the rooftops so that as many people as possible can be in the right place. Naming two could muddy this up (it's already a bit muddy with the beta servers. Eternal Grove? Crystal Desert? Darkhaven? I've had more than a few people message me confused).
If you go as far as to create a temporary "guild" so that your influence isn't wasted (so to speak, it'll be wasted when you move servers anyway) then you lose the social aspect of being in Vanguard. You can only represent one guild at a time and if you're all off in the "back up" server guild, you won't be able to communicate with the rest of the guild. Again this could cause confusion when somebody thinks we only have 10 members in the guild when we actually have a whole lot more.
The initial "cap" for members in the guild is 50. I think we'll hit this almost immediately and thus we'll need to expand to 100 within the first few hours. Being able to expand to 100 members takes 1s and you need to have enough members online and representing your guild to be able to do this. Having 50 members offline or representing other guilds would stop us being able to expand the roster and thus people would be left with no way to get invited into the guild. I'm losing sleep over this because I'm going to invite people as quickly as possible and I'm worried if enough people aren't online we may hit that wall anyway.
Also people tend to make a "home" for themselves and get attached really quickly. If we start making things official and creating back up guilds then we risk creating a splinter faction that we would have to support in the same way we do with Vanguard or risk losing some of our member base completely, this would be more work from an organisational standpoint with no benefit.
I really understand the worry that you'll be left in the wilderness but this is only going to be a problem when the game first launches. I hope to play Guild Wars 2 for years and if a rocky start is what we have to put up with then so be it, it'll all work out in the end.