There is no way to go back to the old look. The needed files are probably no longer on the server.
It is possible to access your Yahoo mail using the POP3 protocol from any e-mail client like Thunderbird from Mozilla or several others.
It's also possible to automaticaly tranfert or forward the messages to another address of your choice.
For both, click the "Option" link at the top of the page.
Sellect "POP and message transfer".
Sellect whitch option you want to use.
If you want to use the POP option, click the blus ? button and click "More info".
It will open a new page with instruction on how to properly configure your client.
To enable the transfert option, just enter the desired address in the box.
Electro, July 2012