... since it's an offline wallet then even if your password was written in your intercepted email, it can't be used to unlock your wallet and change its password without also having your wallet.dat file.
Read the OP again:
Back in 2014 i had a wallet.dat file. I saved in an email as well as in a disk. Somehow after few months someone hacked my email and got hold of my wallet.dat file.
OP had stored their wallet.dat in their email... it was hacked... so likely the hacker had access to the wallet.dat
Although it is impossible to know exactly what the hacker did or did not download, the wallet should be considered compromised and coins moved as soon as possible.
Also, this is surprising:
I had my password written there.
...
Till today those coins have not moved.
So, it would seem that the hacker did not realise they had access to the wallet.dat
and the password to the OPs wallet??!?
In any case, personally, I would be shifting those coins to a new wallet ASAP...