wallet.dat – What if I delete the wallet file but still have my private key

The primary definition and meaning of a bitcoin wallet is that it represents a set of private keys. So I assume you mean deleting such a file.

Whether you will be able to access your wallet again and in what form depends on the type of keys in it.

Those keys can be:

1. linked to each other – HD wallets (deterministic wallets)
2. unlinked (non-deterministic wallets)

Deterministic wallets (HD wallets) are based on the fact that from one master seed, or from a master key previously derived from that master seed, all other keys are derived. Various standards are used for this, the most famous being BIP32. This process is “recursive”, meaning that if you derive from a master key its child keys, then those keys can further derive their children and so on. Therefore, if that private key you know is:

1. master private key – you can again access the complete wallet, i.e. all private keys
2. non-master private key – you can again access only part of the wallet, i.e. all private keys to which that key was a parent in the derivation process

Non-deterministic wallets can be seen as a collection of private keys that reside in one place and those keys are not linked in any way. Therefore, if you know some of the private keys, it will not be enough to access the whole wallet or at least part of it.