An EMP is actually an interesting point. Makes me consider a lead casing for one of my wallet file backups. However, counterfeit BTCs or any sense of wiping out ALL BTCs is highly unlikely. An EMP targeted at one specific location would disrupt the mining network and potentially destroy some people's wallet files but in no way could destroy every single BTC or stop the peers in the network from continuing.
It makes me wonder, what happens to the BTC infrastructure if, say, a country is completely cut off from the outside internet? For example, Egypt during the Arab Spring? If there were enough peers inside that country would they come to a consensus about a particular block and continue the blockchain forked from the rest of the world? Or would the peers in the country not be able to "access their funds" because all transactions would be unconfirmed?
Interesting thought about the EMPs.. what if an EMP wiped out a significant portion of the wallets (and thus currency). With a decent sized chunk, value probably further increases because of supply reduction, but if the chunk were huge, it might crash the currency because of a loss of liquidity.
This brings up an interesting point too, would there be value in a currency which required establishing ownership of coins every X days/months/years. Think of it as a required proof-of-stake, where failure to prove actually means the coins are "reclaimed" by the network and the network parameters are rolled back an appropriate amount. This could allow recovery of "lost" currency. For instance, early in the Bitcoin lifespan, I created a wallet and mined a block or two (when they were still virtually worthless), but then lost my hard drive and forgot about BTC for quite some time. It would be nice if those coins could be recovered and not lost forever...
