Do you have a recent backup from before the deletions / edits? If not you should ask your host if they have one. You can restore the backup and lose recent content since the backup was made. Or you can attempt to selectively restore just those posts. This requires some SQL dexterity.
If there is no backup then you might still be able to do something if the posts were only soft deleted. A soft deleted thread / post involves these database fields:
Soft deletions also always have a record in xf_deletion_log.