Recovering funds after I lost my wallet.dat
If you have your private key, you can add it to your wallet with the command
bitcoin-cli importprivkey "&lt;YOUR_PRIVATE_KEY&gt;" "" false

(The false at the end is to cancel rescan at the moment of adding. It could take some time.) 

If you do not have the private key associated with the address the coins were sent to back then, they are lost.