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From your wording, I think you may be confusing "PageRank" and "rankings". Or did your PageRank (the green bar in the Google Toolbar) also vanish when your rankings did?
One thing you might look into is having a back up site at the ready with all your content loaded and the dns set up on it so u have something to fall back on when you have major outages.
My site was down for about one week. Every internal page lost its ranking bar and ranking on search page. I restored my site about 8 days ago. Today I am seeing many pages coming back on the first pages of search (but not at top as before), some pages has the green bar. It is a good sign and hope it will continue while google is reindex my site.