Yahoo would purge all inbox messages for an inactive email. Hotmail does the same thing.
Gmail is more forgiving. If you are inactive for a year, Gmail won't bother.
How to retrieve? Write to Yahoo customer service. But I don't if you get a personalized response.
Always back up important documents in an external hard disk.
Linkback:
https://tubagbohol.mikeligalig.com/index.php?topic=10897.0