I have deployed DAPP on two node private ethereum blockchain network. According to this question it is not possible to access all accounts across multiple nodes. My question is consider a scenario where a particular ethereum node crashes due to some reason. In that case all account information which is stored on that node will lost. If private keys of accounts are stored safely outside the node then can user will unlock account using his/her private key from other node?
In the Answer to the question you referenced, the key phrase is
without adding your key files there
You can unlock any account from any node, but you have to bring the private key with you. The default is local storage on the node that created the account. Private keys are not replicated to other nodes automatically because you probably don't want that and that wouldn't be "private".
Also, keep in mind that Ethereum is a protocol and the implementation details vary depending on the client (geth, parity, MEW, metamask, hardware wallet, etc.). In geth, for example, keys live in the
keystore folder under
.ethereum and the private keys are encrypted by a passphrase. You will need the keystore file and the passphrase. That's done for you, as long as you continue using the same node. To move to another node, all that's really needed is the keystore file and the passphrase.
The steps to import/export keys will differ depending on your node and client preference. The common element is the account owner presents the secret key.
Hope it helps.