If you have deleted your wallet application or if something happens to the hardware wallet, you can not recover a private key. You can always retrieve a private key with a seed value (12 to 24 mnemonics). It’s important to understand, your bitcoins are lost forever, unless you have the key. There is no way to recover your bitcoins without the key. There are rare cases where people have recovered keys from their damaged hard drive. Sometimes, if you remember at least parts of the code (it depends on the wallet you had), it can be brute-forced. But that would only be practical if you lose hundreds or thousands of bitcoins. No hacker, no tools and no special trick will give you these funds back without the key.