I accidentally deleted the category. Is it possible to bring back the messages again?
No hosting backup.
Welcome to the community.
It is not clear what you have done.
If you have only deleted the category via the Dashboard, you should be able to restore the discussions to it if you recreate it.
There are 3 separate tables involved:
comment, discussion, category
This assumes it gets the same ID number it had previously.
If it doesn't, you will need to edit the category in the DB to match whatever the original number was.
You should be able to find that by looking at a discussion you know was in that category.
If you manage to do this MAKE A BACKUP, OFFSITE, OF YOUR DB!