DDOS Safety Electrum?
I'm not exactly sure if this is what you're asking; nevertheless the wiki says: 


  Transactions are signed locally: Your private keys are not shared with the server. You do not have to trust the server with your money.
  
  Freedom and Privacy: The server does not store user accounts. You are not tied to a particular server, and the server does not need to know you.


It seems the storage of your keys is client-side, so if they were to get (D)DoS'd you could easily move you keys to another wallet.