This is one of the advantages to having a multi-sig wallet where you need multiple keys to sign a transaction instead of just one. Having a single key represents a single point of failure. Of course you still need to manage your keys in a multi-sig setup, but you don't risk ruin if you happen to lose one of the keys (if for example you had a 2 of 3 setup which means you have 3 keys but need only 2 to sign a transaction).
You will need to understand what multisig wallet is, this is only good when there are many people that needs to handle a single wallet, a good example is of a company want to have a bitcoin wallet that needs to be handled by many people, the company can have a multisigwallet in a way two or more users can be given different private key. In this case, if any of the private key is compromised, the bitcoin on the company wallet can be sent to another wallet which they have just newly generated without anything happening.
If you have a multisig wallet, do you know the transaction fee is higher than normal wallets? That aside, many people will still have to do the backup together which can make the multisig wallet to be hacked at ones if hackers have access to the backup.
There are many people making use of cold wallet backup and yet their wallet is safe.