My pc suddenly and I was forced to replace old HDD with a new one. After Windows reebot I tried to reclaim Witcher 3 save files from the old HDD. Where can I find them? documents-> The Witcher 3 -> contains only input.settings, user.settings and user.settings.bak. My gameplay was several hours long and I finished Skellige plot.

try C:\Users\<ur username>\OneDrive\ and there documents\The Witcher 3 there should be "gamesaves" folder
or if you had synchronized ur Microsoft account with onedrive, then log in to onedrive and synchronize ur data