Windows Backup
The built-in Windows backup tools are a little hit and miss. For instance it is not possible to easily restore just one partition using the Windows 7 Backup and Recovery tool. This is a real problem because WinRE only contains Windows 7 Backup and Recovery.
Windows Server has 3 backup utilities:
Windows 7 backup and recovery (which is stored on the WinRE partition). This can only restore all partitions in one go. It also requires the exact same hardware to restore to.
Windows Server Backup (snap-in) wbadmin.msc. This GUI tool will restore just the partitions. This needs to be run from a full copy of Windows 2012, it doesn't seem to run from WinRE that easily. I used this to restore the server last time, by installing vanilla Win2012 first, then appmgr.msc > Add Features > Windows Server Backup features.
Windows Server Backup (command line) wbadmin.exe. This command line tool will restore just the partitions. https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/wbadmin-start-recovery. This is available on Gandalf's WinPE iso.
After you recover a partition only, you may need to do the following:
https://support.microsoft.com/en-au/help/927392/use-bootrec-exe-in-the-windows-re-to-troubleshoot-startup-issues. This requires booting from a WinRE disk.
I recommend running all commands:
bootrec /ScanOs
bootrec /FixMbr
bootrec /FixBoot
bootrec /RebuildBcd