What happens to unapproved transactions?

[DannyHamilton]

What i do not understand is how can a transaction registered in block be returned if it was found that it was a zero fee transaction.

It cannot unless that block becomes orphaned.

And is it possible for the miner to proceed with the transaction even with a zero fees if he wants to.

Yes.

Will there be any core updates from the developers to tackle the transaction delays.

Pay a higher fee.  You'll have less of a delay.

[voltesbit777]

Let's assume we entered the value of the fee too low in a process we have done. You can even get the value of the fee 0.
Miners receive transaction fees as rewards for transactions they approve. They approve higher transaction fees earlier.

What happens if our zero fee entry is not approved at all? Is there such a possibility? Or how long will it be approved at the latest?

Transaction gets dropped and coins return to original sending address.

The timing depends, transaction may be rebroadcast.

Yes true and correct, But usually this happened to those people who gave small low fee's in the blockchain. I remembered in the other nation told give 1$ for the charge fee for you to be prioritize.