Bitcoin network works on a Peer-to-peer mode, so "taking the network down", would require taking at least a good portion of the Internet. Should something like this happen, Bitcoins might not be the biggest of your worries.
A Bitcoin miner stores little to no information about the network itself. It works in a simple terms of fetching data, calculating some hashes and returning results. It does not need much more than that, so miners going offline for awhile wouldn't hurt the network much, asides slowing down block generation for awhile.
A Bitcoin client on the other hand stores all the data from the Bitcoin network. Should it go offline, it still stores all the data on the hard drive and will try to reconnect when it can. Should a good chunk of the network go offline, the blockchain might fork, as each part of the network would try to work only with the data it possesses. Some parts of the network might see only a part of the transactions, while others would see other transactions. When such "islands" would meet, all the clients will try to establish which blockchain is the longest. The shorter blockchain will have all its transactions extracted from it and if there is no double-spend, those transactions might be included in future blocks.
All in all, it is very hard for the Bitcoin network to go down, and the main Bitcoin client is prepared for possible network segmentation.