[M.C.]

My way of doing that:

Go to your phpMyAdmin
Open your DB and go to "post" table
Find any post your user did (you can do it by "postid" or any other creteria)
There are "Username" and "userid" columns - you need to remember them.
Then go to "user" table, find your new created user (usualy at the very end of table)
Click "Edit" and change his new "Username" and "userid" with old one from "post" table
Save

Now you can go in your Admincp and find all soft deleted posts by username and recover them

No need to roll back your database.