Is it possible to run a Bitcoin Miner offline and calculate hashes without being connected to the Internet?
You cannot earn Bitcoins mining unless you either add blocks to the blockchain or cooperate with others to do so. Without being online, you wouldn't know the current head of the blockchain (or any information based on it), so there's no way you could actually do either of those things. You could hash all you want, but you would never mine a block nor contribute towards mining one, so there wouldn't really be any reason to do so.
Yes you can, but the whole point of hashing is to share the results with the blockchain which can only be done while online. Without sharing results there is a very big chance you are calculating the wrong transactions--transactions which have already been hashed by someone else.
It would be like mining gold inside a mountain but never bringing it to the surface. Why bother?