Hi Welcome to JustAnswer
If you have already submitted the request for lost folders then you should be able to retrieve it.
No, In mail version of yahoo we do not have a copy of emails stored in pst files as in outlook.
I would recommend you to change your security answers,your password ***** update your phone number in yahoo if you have not done already. As there is a possibility that someone might have got unauthorized access to your mail box
Let me know if you need any help on this and if you want me to take remote access of your computer and help you in it.
I think your issue must have been resolved by now. Do you still have this problem ?