Am I safe forever if I backup this file and not an actual backup? Or paper backup?
The backup is an extra file used to perform drive IO operations twice. It's main purpose is to confirm data was properly written to the wallet. The backup and its designated wallet carry the exact same information.
You can save either the wallet file or its backup, or both. Paper backups allow you to recreate deterministic wallets. It guarantees you can reproduce all the possible key pairs your wallet can yield. Keep in kind that a paper backup does not carry information about imported private keys, as those were not produced in a deterministic fashion, using the wallet's rootkey and chaincode.