What happens if my network goes down? Will I still be able to search?

As long as you can still access your Google Mini over your network, you will be able to perform searches. The Mini won't be able to crawl any unavailable servers, but it can still serve up the search results. The search results contain a lot of information about the document, and there will even be a cached HTML copy, just like with Google.com. While the Mini isn't as comprehensive as a full backup solution, it is probably a lot less work than digging around in a backup server during a temporary outage.