Windows is unlikely to lose Word itself. It's far more likely that it's simply the shortcut to it which has disappeared and/or the file association which links .docx files to it has become corrupted.
Double-click on the icon for one of your Word files. If it opens normally it's simply that the shortcut (on your desktop and/or on your Start menu) has disappeared. Click to open the Start menu and see if you can find it listed there. Remember that it might be listed under 'Microsoft Office', rather than simply as 'Microsoft Word'. If you find it, RIGHT-click on it and then on Send To > Desktop.
If the file doesn't open in Word, and you see a message telling you that Windows doesn't know which program to use, click on the option to select an appropriate program (ensuring that the option to 'always use this program . . .' is ticked).
If something else happens, please tell us.
If all else fails, forget about using Microsoft Word altogether. You don't need it. Most AB members don't use it anyway. The most popular alternative here, without a doubt, is OpenOffice. (It's what I use):
https://www.openoffice.org/
LibreOffice is also popular among ABers:
https://www.libreoffice.org/
WPS Office is less well-known but is equally well-reviewed in the technical press:
https://www.wps.com/office-free