the safest wallet is the offline wallet but there is still a risk that if the pc where you keep the offline wallet is destroyed then you can not do anything, print the wallet on a old printer with no internet connexion and no memory, then you can still lose the paper, so there is no safe, there is always a risk
if you hold a massive amount of coin in your offline wallet, you should make it valuable, secure it privately and encrypt it. keep it in a safe place. that's should reduce the risk and if you really think its valuable you should make it as importance thing.