Re: Reinstall Windows 8.1
While it's always a good idea to have a backup, backing up to an external drive wouldn't be a requirement here as it's on a drive he isn't wiping clean.
Ignoring Steam for a second, you'd still need to reinstall the programs. They create registry files and other system entries that would be lost in the reinstall. You could back up the registry but you'd likely be copying too much which defeats the point of the reinstall.
Back to Steam. Last time I reformatting was right after steam started saving to the D drive if setup. I found that after steam was reinstalled and pointed to the original install folder (where steam puts all of it's games) then it picked them up. What might not be a bad idea though if you have the storage space for it, is to back up the games installed in Steam (File, backup and restore menu). That way if you do need to reinstall the games, it's just a quick restore and not a long process of individual downloading.
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