Once i had that problem during a hosting change. Site was on and off over a week. There was some demotion on SERP for a while, then they came back.
So if anyone is curious, my site was down for 5 hours yesterday from about 3 PM to 8 PM CDT. Today my position #5 in google on a keyword term has disappeared from the top 50 (I stopped looking after that). I have been on the first page for nearly 6 months. My guess is it will be back shortly. (hoping). But wow google works fast.
lol... since most people on DP seem to be crying about PageRank... I'll document that it looks like my SERP's are back (at least from my searches). Traffic seems to be there now. So for my site being down 5 hours one evening, I lost about 1/2 day from my page 1 listing on google. Someone may find that interesting.
it takes for long for established site (the site that exist quite long time) and even it got deindexed(seems,but not, just place to supplemental), you can still find the page by site: bottomline, google cache will always there, so if google still want to let people visit cache, it has to be in SERP somewhere
The higher your site rank, the more frequent it gets updated and indexed by Google. Lower ranked websites willl survive longer (That's just my experience. I have page 1 site that was url redirected but still not deindexed)