Robert_Charlton - 10:56 pm on Nov 1, 2012 (gmt 0)

Regarding SEO implications, I'd get a custom 503 unavailable page up there asap, to avoid 404s that might get your backlinks deleted, and to preserve status with the engines. The custom 503 should be a very nice page to explain the situation to all who access your site, provide contact info for your users, etc.

I'm not sure how long you can return a 503, but prolonged 404s are likely to hurt.