As others have said, you really can't be sure what Windows will automatically detect and what it won't. It is likely for some devices, like the audio or graphics card, it MAY install a basic driver providing basic functionality. Of course, in any situation, you should always make sure your drivers are correct, and at their most current.
If the system is still operational, I would recommend looking at the drivers right now for all of your important devices. If you know the exact brand and model and everything, you can look for drivers right now and store them on a disc or flash drive, ready to install once you reformat.