If you don't format your D drive,the games you had will be there after the OS re-install.
What it's doubtless is that your fresh OS will need the games' requisites ASAP for the games to run.
Once with the procedure,I recommend keeping games' setup files before letting the ''new'' OS making the deal (before making the fresh OS install)
Why?
Even if it has its software requirements accomplished,any game won't run without introducing its specific installing files into the OS drive (C).
Running the games' setups to re-update the games' files (back-up your saves from the games in a cloud storage service before this) will assure you the games will work again.