emails deleted from yahoo inbox

What a near impossible question to answer but if the messages have been deleted from the server and they don't appear in the deleted box then NO they can't be recovered.

Yahoo does retain backups for a limited time. Your friend will have to contact Yahoo and explain what happened.

Don't wait too long though, it's a short backup retention period.

Try this: Restore missing emails or IMs

yahoo said:

In some cases, we can restore lost or deleted emails and instant messages (IMs) in Yahoo Mail. Here's how to request a restoration attempt.

Before requesting a restore
•We can only restore emails and IMs that were lost within the last seven days.
•If multiple restore requests are submitted, only the latest request will be processed.
•Back up any emails sent or received within the last seven days.
- These emails will be permanently deleted if the restore is successful.
•To back up IMs, you'll need to copy/paste them from your Conversation History into a text document.

Submitting your request
From a desktop or laptop, use our restore request form if you'd like us to attempt to recover your missing emails or IMs.