I am not really sure what you mean, but let's start in one end: By root folder, do you mean the archive folders? If so, then yes, you can make a new server installation use the old archive. You can use the descriptions for moving servers in the PDM Installation Guide.
As for backups, you should have a backup of the archive files, and the database. Without the archive, you have nothing.Without the database, you have a lot of work. The main point is, if you have the backups, or are able to retrieve the files, you can restore your system completely. Also, for disasters i would contact my VAR for their assistance asap.
This is actually a pain in the butt. The simplest way is to use the archive backup and restore it. This is something you'll want to do with help though, and make sure you have copies of the archive folders, inc case anything goes wrong. Martin Solem nails it, and the PDM installation guide (https://files.solidworks.com/Supportfiles/PDMWorks_Ent_Installation/2017/English/Installation%20Guide.pdf ) can help some guidance on it, but you'd be best to work with your VAR on it, or seek our PDM specialists like InFlow Technology (www.inflow-tech.com) to help out with it. I'm a PDM consultant, and do this kind of work day in and out.
Your archive configuration tool will be the way to restore the archive folders and connect them to your SQL database, but again, I'd contact your VAR or a PDM specialist.